1. Influence of ink viscosity
The viscosity of the ink should match the printing speed. When printing at high speed, the viscosity of the ink should be controlled between 12 and 15 seconds (3 # Zahn Cup); when printing at medium speed, the viscosity of the ink should be controlled between 16 and 18 seconds (3 # Zahn Cup). The viscosity of the ink is too high, and the adhesion to the plate cylinder is too strong, which is not conducive to the scraping knife to scrape off the excess ink on the plate, and the probability of a knife line on the printed product is high. During the printing process, the ink viscosity should be measured and controlled at regular intervals, generally every 20-30 minutes.
2. Influence of ink drying
The ink dries too quickly and is prone to skinning. If the skinning is not dissolved during the ink circulation process, it will stick to the blade or the bottom of the blade once it contacts the squeegee, resulting in a print line. If the ink circulation system uses an open ink tank, ink caking and caking are more likely to occur. In order to reduce the occurrence of such knife line faults, 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 knife line faults.
3. Influence of ink fineness
Gravure ink is mainly composed of pigments, binders, additives and other components. If the pigment is not sufficiently ground, the particles are coarse, and they are insoluble in the binder and solvent, and stay at the squeegee blade during printing, it will cause small, irregular knife lines in the print. The fineness of the pigment particles has a direct impact on the appearance of the knife line. For example, the pigment particles used in blue ink have high hardness, and even after sufficient grinding, it is difficult to achieve a very fine particle size, and it is easy to damage the ink during the printing process. The knife may affect the effect of scraping ink, and the knife line often fails when printing blue ink.
4. Influence of ink activity
In the production process of ink, a certain amount of active agent is generally added. The plate cylinder also has a certain activity after chrome plating. If the activity of the ink and the plate cylinder is too high, the active substance will firmly adhere to the cylinder during printing, and it is difficult for the doctor blade to scrape it off, thus forming a knife line. At this time, first clean the plate cylinder to remove the active substances on the surface, and add an active retarder to the ink to eliminate the knife line.
5. Influence of ink quality
If the ink storage time is too long, the solvent balance will change, resulting in a decrease in the solubility of the ink; or the ink is improperly formulated and used, causing a chemical reaction, which will cause the ink to precipitate. In the printing process, the deposits in the ink are easy to accumulate in the blade of the doctor blade and cause the knife line, so the ink needs to be replaced.
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