The leveling properties of PE screen printing inks are closely intertwined with pigment dispersion. This relationship permeates the entire process of ink formulation design, printing process control, and final film quality. Pigment dispersion directly influences the ink's rheological properties, while leveling, the ink's ability to spread autonomously on the substrate surface to form a smooth film, is crucial for achieving defect-free printing by eliminating surface tension differences. These two properties form a dynamic balance within the ink system.
Pigment dispersion is a key factor in determining the ink's initial flowability. In PE screen printing inks, pigment particles must be refined to submicron levels through a grinding process and uniformly dispersed in the binder. Insufficient pigment dispersion can lead to particle agglomeration, forming large aggregates. These aggregates hinder molecular chain slippage during ink flow, causing an abnormally high viscosity and manifesting as increased thixotropy. Consequently, the ink must overcome greater internal friction during transfer to the screen, which can easily result in blurred edges or uneven ink layer thickness, directly weakening the foundation for leveling.
Analysis of the leveling mechanism suggests that pigment dispersion regulates the film formation process by influencing the surface tension gradient. Highly dispersed pigment particles are evenly distributed throughout the ink film, ensuring consistent surface tension changes during solvent evaporation. When pigments are unevenly dispersed, localized differences in surface tension due to varying pigment concentrations can cause the ink to flow toward areas of lower tension, leading to "craters" or "orange peel" defects. For example, in screen printing on PE containers, if undispersed titanium dioxide particles are present in the ink, visible protrusions will form on the film surface after drying, disrupting the overall smoothness.
The synergistic effect of pigment dispersion and the thixotropy of the ink further influences leveling. Thixotropy refers to the property of an ink that decreases in viscosity under shear and recovers after resting. Highly dispersed pigment systems form a more stable colloidal structure, enabling the ink to level quickly under squeegee shear while maintaining sufficient viscosity to prevent run-off. For glossy printing on PE film, this property ensures that the ink quickly recovers after passing through the screen, avoiding the inadequate leveling time associated with excessively high thixotropy.
Matching printing process parameters with pigment dispersion is crucial for optimizing leveling. In PE screen printing, screen mesh size, squeegee hardness, and printing speed must be adjusted based on pigment dispersion. For example, when using highly dispersed inks, a higher mesh size (e.g., 350-420 mesh) can be used to print fine patterns, while a medium-hardness squeegee (70-75 degrees) can be used to ensure even ink transfer. If the pigment is insufficiently dispersed, the printing speed must be reduced to extend the leveling time, but this compromises production efficiency, highlighting the importance of controlling dispersion.
The introduction of additive systems provides a technical solution for balancing pigment dispersion and leveling. The addition of polymer dispersants creates a steric barrier on the pigment surface, preventing particle reaggregation, thereby maintaining high dispersion while reducing system viscosity. The addition of leveling agents can selectively adjust the ink's surface tension, eliminating local tension differences caused by uneven pigment dispersion. In the PE8723 series of premium gloss screen printing inks, the synergistic effect of these additives achieves a balance between high dispersion and excellent leveling.
In practical applications, the relationship between pigment dispersion and leveling requires systematic process verification. For example, in screen printing production of PE turnover containers, control standards must be established for the entire process, from pigment grinding and ink mixing to printing parameters. Regular testing of ink fineness (e.g., using a scraper fineness meter) and leveling time (e.g., using a flow meter) can quantitatively assess the impact of dispersion on leveling, providing data support for process optimization. This systematic control is the core guarantee for achieving high-quality leveling results with PE screen printing inks.
