Problem 1: Coating Defects Coated and uncoated films are commonly used in printing, and coating defects can lead to ink dropout. For coated films, poor adhesion of the surface coating may result in ink loss during printing. On the other hand, uncoated films often suffer from weak ink adhesion due to insufficient surface fastness. To address ink dropout caused by coating issues, several solutions can be applied. First, applying a varnish layer on the surface can protect the ink and improve its adhesion. Second, corona treatment is recommended to increase the surface energy of the material, with a dyne value of at least 38 mm/m. If the dyne value drops below 36 mm/m, it can significantly affect ink adhesion. Additionally, using a primer or an ink enhancer (with a concentration of around 3%) can enhance ink adhesion. Some synthetic papers with a paper-like surface may not be suitable for 3M tape testing, as their coatings behave differently. Problem 2: Corona Treatment and Ink Wetting For films that have been corona-treated, achieving good ink wetting requires a dyne value above 38 mm/m. If the value falls below 36 mm/m, ink dropout is more likely. Moreover, the dyne value tends to decrease over time, which can lead to ink loss during printing. This issue is essentially related to surface tension. To resolve this, online corona treatment using a satellite rotary press can maintain surface energy. Alternatively, intermittent printing machines with primer coating can improve adhesion. When the dyne value decreases, re-corona treatment during printing is necessary. However, the dyne value doesn't always reflect the actual ink-to-material adhesion, as it typically fades within 3–6 months. Therefore, it's advisable to minimize long-term storage of raw materials. Using inks with higher adhesion is also recommended, and consulting with ink suppliers is highly advised. Problem 3: Ink Drying and Tension Ink drying and tension during the printing process can also cause ink dropout. Common causes include excessive ink layer thickness, which leads to incomplete drying. UV lamps with insufficient energy, aging lamps, or dirty reflectors can fail to cure the ink properly. Additionally, overly dry ink may cause material deformation, resulting in ink coming off. Solutions include using deep ink with thin layers—reducing the amount of ink applied while increasing UV lamp output and slowing down the printing speed. Checking the UV lamp’s condition and cleaning the reflector regularly (every six months) is essential, as domestic UV lamps usually last 500–1000 hours, while imported ones can last up to 2500 hours. Lastly, adjusting the UV lamp power to avoid over-irradiation is important, especially for delicate film materials, as excessive heat can cause curling, brittleness, and reduced ink adhesion. Problem 4: Ink-Material Compatibility The compatibility between ink and material can also contribute to ink dropout. For example, if the ink has high molecular tension, it may not spread evenly on the substrate. Using expired or low-quality domestic inks can also lead to ink loss. To solve this, switching to inks specifically designed for the material, such as film-compatible or light-fast inks, is recommended. Testing is crucial before full-scale printing, especially when using expired inks. Printing simple text or small logos first can help identify issues. For large solid areas or complex patterns, high-quality inks with strong adhesion, like Hangzhou Hua ink, are preferable. Summary of Factors Affecting Ink Dropout Through the analysis above, we can summarize eight key factors that lead to ink dropout: 1. Poor surface coating fastness on coated films. 2. Weak surface fastness on uncoated films. 3. Low dyne value on corona-treated films (below 38 mm/m). 4. Dyne value fading over time (3–6 months). 5. Thick ink layers and insufficient UV curing. 6. High ink tension leading to uneven drying. 7. Use of expired or low-quality inks. 8. Over-drying or excessive UV irradiation. By addressing these issues systematically, print quality can be significantly improved, ensuring better ink adhesion and fewer production problems.
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