Three kinds of printing faults and preventive measures after printing

Fault 4 shrink hole

Cause: Shrinkage is one of the problems that occur due to the poor leveling of ink film in printing ink. The wet ink film of the printed product appears retracted during the leveling process, forming a small film shape with bare substrate or bottom ink layer exposed. This is due to the different surface tensions of the upper and lower parts of the wet ink film. The wet ink can be regarded as a double-layered liquid film. In the post-press filming process, shrinkage occurs when the surface tension of the upper wet ink film is lower than the surface tension of the lower wet film. It can also be explained as the cohesive force rebound caused by too much plasticizer in the printing ink, shrinkage occurs. Occasionally, when this phenomenon is about to occur, the wet ink film loses its leveling property, just suppressing the occurrence of shrinkage holes. In some fast-drying gravure, thermosetting offset or screen printing, when the temperature of hot air or baking temperature increases, the ink film is leveled again, resulting in secondary shrinkage.

Preventive measures: Improve the flowability of the ink, reduce the surface tension of the ink, and ensure the wettability of the substrate. Leveling aids or low surface tension solvents can be added. At the same time, the surface of the substrate should be treated to improve its wettability. For example, before the printing, the surface of the substrate can be cleaned with a solvent, a rag, or an electric spark.

Fault five spots

Cause: Spot (also known as graining) is the generic term for irregular blockages on the ink film surface after printing. The spots are caused by poor dispersion of the pigment, insoluble polymer particles in the binder, or precipitation of insoluble metal salts, and the disintegration of small pieces of ink into ink. Dust is also the cause of spotting in the air of the printing shop or the surface area of ​​the substrate. In addition, the roller coating compound is not uniform, once the composite substrate surface will form irregular spots, especially the composite of pure aluminum foil is more obvious.

Preventive measures: Pay attention to the dispersion and purification of printing inks and increase the cleanliness of the printing shop.

Failure six

After printing, the ink film at the sheet corners retracts, causing the ink film at the location to be thin and even exposed. This failure is another form of shrinkage. Due to the high surface tension of the wet ink printing film, the surface energy of the system tends to be minimized, and the wet ink film retracts from the corners.

Preventive measures: Use as little as possible sharp corners, sharp edges, chamfers, and edges in the layout. A thixotropic agent is added to the printing ink to increase its fluidity and extend the leveling of the ink film.