Due to the thicker ink layer in letterpress printing,it is more prone to printing ink drop. What are the common causes of “ink drop” in printing?
1. Material Surface Tension
Printing materials have surface tension. Generally speaking, the higher the printing materials’ surface tension, the better the ink fastness after printing. Most paper-based materials have no problem with surface tension, but film-based materials tend to have uneven surface tension.
Therefore, when we print film materials, we need to test the surface tension of the material. If the surface tension of the material is too low, we need to perform corona treatment on the machine. It should be noted that some film materials have their own surface coatings in order to improve the ink adhesion. Generally speaking, the materials treated with the surface coating can be more firmly combined with the ink.
2. Printing Ink Matching Problems
At present, there are many types of letterpress printing inks, and the ink from one manufacturer also have multiple series. Some inks are specially developed for low surface tension materials. Therefore, when we print materials with low surface tension and we don’t have equipment with corona function, some targeted inks can also be used to solve the problem. It should be noted that before selecting ink, it is best way to send the material to the ink supplier, ask them to do the test, and use it after the test result is no problem. Because not all materials can be perfectly matched with the ink.
3. UV lamp drying problem
At present, most letterpress printing equipment uses UV lamps for drying. If the power of the UV lamps is insufficient, the phenomenon of false drying may occur. This is because the letterpress printing ink layer is thick, especially for some large-area solid patterns. Thick ink layer is not easy to dry. If the power of the UV lamp is insufficient, it is likely that the surface of the ink is dry but the inside is not dry. This phenomenon is especially common in patterns with darker colors. Because dark-colored patterns are more effective at absorbing UV light, they tend to require more power to dry thoroughly. Therefore, when printing large-area real-world graphic products, it is necessary to use tape to test the ink firmness. If the ink is sticked off, the firmness is unqualified. At this time, the power of the UV lamp needs to be increased. In addition, the current life of UV lamps on letterpress printing equipment is between 800 and 1000 hours. If the lamp is not replaced when the rated life is exceeded, it is easy to cause the ink to dry.