How can the leveling properties of Flexo water-based ink for tableware be optimized to improve the smoothness of the printed surface?
Release Time : 2026-01-07
The leveling property of Flexo water-based ink for tableware is a core factor affecting the smoothness of the printed surface. Its optimization requires comprehensive adjustments from multiple dimensions, including ink formulation design, printing process control, substrate pretreatment, and the synergistic effect of additives. Leveling property essentially refers to the ink's ability to automatically spread and form a uniform film on the substrate surface. Insufficient leveling property can easily lead to defects such as orange peel, pinholes, and streaks after printing, resulting in decreased gloss on the tableware surface and even affecting food contact safety. Therefore, optimizing leveling property needs to focus on the ink's rheological properties, drying mechanism, and compatibility with the substrate.
Ink formulation design is the foundation for optimizing leveling property. The resin binder for Flexo water-based ink for tableware should be a low-viscosity, high-flexibility water-based acrylic or polyurethane resin. These resins have highly mobile molecular chains that can quickly fill the microscopic unevenness of the substrate surface, reducing ink flow resistance. Simultaneously, the fineness of the pigment particles needs to be controlled below 10μm and uniformly dispersed to avoid "bridging" during the leveling process due to particle agglomeration. In addition, an appropriate amount of leveling agent, such as silicone leveling agent or acrylate leveling agent, needs to be added to the formulation. These additives can form a monolayer on the ink film surface, reducing the surface tension gradient and promoting uniform ink spreading.
Precise control of printing process parameters has a significant impact on leveling properties. In flexographic printing, the line count, angle, and ink layer thickness of the anilox roller directly affect the amount of ink transferred. If the line count of the anilox roller is too low and the ink layer is too thick, the ink layer may shrink unevenly during drying due to rapid solvent evaporation, resulting in surface defects. Conversely, if the line count is too high, it may lead to insufficient ink transfer and incomplete ink coverage. Therefore, appropriate anilox roller parameters must be selected based on the surface roughness of the tableware material (such as ceramic, glass, stainless steel, etc.). Simultaneously, the printing speed must be matched with the ink drying speed to avoid the ink layer entering the drying stage before leveling due to excessive speed, or the ink layer becoming excessively fluid and causing blurry patterns due to excessive speed.
Substrate pretreatment is a key step in improving leveling properties. Tableware surfaces often have oil stains, oxide layers, or microscopic scratches, which can disrupt the continuity of the ink layer. Therefore, the substrate must be thoroughly cleaned before printing, and surface energy should be increased through methods such as corona treatment, plasma treatment, or primer coating. For example, after corona treatment, the surface tension of ceramic tableware can be increased to over 50 mN/m, allowing the ink to better wet the substrate and reducing pinholes. For metal tableware, applying a water-based primer not only enhances adhesion but also fills surface micropores, providing a smooth printing base for the ink.
The synergistic effect of additives can further optimize leveling. In addition to leveling agents, the use of defoamers is also crucial. Air bubbles are easily generated during ink stirring or printing. If these bubbles remain in the ink layer, they will form pinholes after drying, damaging the surface smoothness. Therefore, an appropriate amount of silicone or polyether defoamer needs to be added, which can quickly diffuse in the ink and destroy the bubble film without affecting the ink's leveling properties. Furthermore, the addition of slow-drying or fast-drying agents needs to be adjusted according to the printing environment. In high-temperature and high-humidity environments, excessively rapid ink drying can lead to poor leveling. In such cases, adding a small amount of slow-drying agent can extend the open time. Conversely, in low-temperature and low-humidity environments, fast-drying agents are needed to accelerate drying and prevent excessive ink flow.
Optimizing the drying process has a profound impact on leveling properties. The drying of Flexo water-based ink for tableware involves three stages: evaporation, absorption, and curing. An improper drying curve can lead to a skin forming on the ink surface while the solvent remains internally, creating a "dry outside, wet inside" state, ultimately causing ink cracking or decreased adhesion. Therefore, a segmented drying method is necessary: first, low-temperature pre-drying to achieve initial leveling; then, high-temperature accelerated drying to promote solvent evaporation; and finally, low-temperature curing to ensure ink stability. Simultaneously, the airflow and temperature of the drying equipment must be evenly distributed to avoid localized overheating or undercooling that could lead to differences in leveling properties.
Controlling the ambient temperature and humidity is an external condition for ensuring leveling properties. The viscosity of ink is sensitive to temperature. Increased temperature leads to decreased viscosity and improved leveling properties, but excessively high temperatures cause the ink to dry too quickly, inhibiting leveling. Conversely, excessively low temperatures increase viscosity, making ink transfer difficult. Therefore, printing workshops must maintain constant temperature and humidity, generally controlling the temperature between 20-25℃ and the humidity between 50%-60%. Furthermore, ink should be placed in the workshop before use to allow for temperature equilibration, preventing viscosity fluctuations caused by temperature differences from affecting leveling properties.
Long-term storage and maintenance are crucial for the stability of leveling properties. Improper storage of Flexo water-based ink for tableware can easily lead to sedimentation, layering, or skinning, resulting in decreased leveling properties. Therefore, ink should be stored in a sealed container in a cool, dry place, avoiding direct sunlight and high temperatures. Before use, it must be thoroughly stirred, and its viscosity, pH value, and other indicators should be checked regularly to ensure they meet printing requirements. Leftover ink should be sealed and labeled with the use date to prevent performance degradation due to long-term storage. By taking the above comprehensive measures, the leveling properties of flexo water-based ink for tableware can be significantly optimized, the smoothness of the printed surface can be improved, and the dual requirements of safety and aesthetics for food packaging can be met.