Study of ink rheology on droplet state and printing quality via simplified Z-value assessment
摘要
The Z-value can comprehensively quantify the viscosity and surface tension of ink, indicating the relationships among ink rheological properties, ink jetting behavior, and printing quality, while effectively simplifying the screening process of ink samples. In this work, the Z-value was employed as a key metric for the comprehensive evaluation of inkjet printing quality. The coupling relationships between ink rheological properties, ink jetting behavior, and printing quality were systematically investigated, and their underlying influence mechanisms were revealed. The high-speed imaging was employed to quantitatively characterize droplet state through critical metrics including tail length, jet velocity, and out-of-roundness. Furthermore, the multi-dimensional printing quality evaluation system was established, which included point (point diameter expansion ratio, point aspect ratio), line (line width expansion rate, line roughness, line blur degree) and solid area (color density). The study reveals that reducing droplet tail length, maintaining moderate jet velocity, and achieving optimal out-of-roundness significantly decrease ink spreading on substrate, improve line edge definition, and enhance color density. The results demonstrate that when the Z-value is optimized within 1.5–2.7 (corresponding to viscosity 8.0–11.0 mPa·s and surface tension 23.0–25.5 mN m-1), both droplet ejection dynamics and overall printing quality reach optimum performance. This study uses the Z-value to comprehensively quantify and characterize the rheological properties of inks, providing an effective method for various functional inks to achieve stable inkjet states and excellent printing quality.