1. Printing Plate
The printing plate is typically created using either electronic engraving or laser engraving techniques. The depth of the etched cells ranges between 15 to 25 micrometers, which is shallower compared to solvent-based intaglio plates. This design is necessary because water-based inks use tap water as a main component, and since water has a higher boiling point than solvents, it evaporates more slowly. As a result, a shallower plate helps increase printing speed and reduces the occurrence of water ripples. In contrast, when using solvent-based inks, the plate depth is usually around 35 to 40 micrometers, which can lead to more water ripples. However, even with a plate depth over 25 micrometers, water ripples may still appear if not properly managed. Therefore, selecting the right printing plate is crucial for optimal performance. During operation, the ink's viscosity can be adjusted by adding water, and for Tu-4 ink, the ideal viscosity should be maintained between 15 to 25 seconds at 25°C. If the viscosity is too high, the ink transfer becomes inefficient, leading to issues like plate fouling or ink buildup.
2. Effective Drying Equipment
Drying temperature must be carefully set based on the type of substrate and the size of the printed area. For example, when printing on aluminum foil labels for wine bottles, the drying temperature should be above 100°C. For plastic films, the recommended temperature range is 50 to 60°C. Additionally, the air flow during drying should be stronger than what is used with solvent-based inks. This is because hot air helps accelerate the evaporation of water from the ink, allowing it to transfer smoothly onto the substrate and dry quickly. Proper drying is essential to prevent smudging and ensure the final print quality remains sharp and consistent.
3. Surface Treatment
Except for materials such as aluminum foil, vacuum-aluminized film, and paper, most plastic films require an electric spark treatment before being printed with water-based inks. This treatment increases the surface tension of the film to at least 0.04 N/m. Water-based inks have a surface tension of approximately 0.072 N/m, so there is a noticeable difference between the ink and the substrate. This mismatch can affect adhesion, making it harder for the ink to stick properly. By increasing the surface tension of the plastic film through treatment, the adhesion of the printed image improves significantly, ensuring better durability and clarity of the final product.
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