毛管状容器に充填されたコロイド溶液の蒸発に伴う断面内粒子拡散係数分布の経時変化の可視化技術の開発

抄録

This paper presents a technique for directly observing the increase in ink viscosity as ink solvent evaporates from an inkjet printhead. Depending on the balance between the generation of a solvent concentration gradient due to ink solvent evaporation and the diffusion that flattens this gradient, the ink viscosity may increase across the nozzle or only near the gas-liquid interface in particular. For printers using single-pass on-demand inkjet printheads with water-based pigment inks, it is necessary to understand the characteristics of such ink thickening phenomena in order to achieve high reliability and low ink wastage. To achieve this objective, a combination of dynamic light scattering and optical coherence tomography was used to observe the distribution and temporal changes in the motion of particles contained in the ink filled inside the nozzle, and to observe the thickening process in-situ. In particular, we attempted to understand the characteristics of the thickening phenomenon that occurs in ink as a result of evaporation by capturing changes over time in the particle diffusion coefficient and its distribution in the nozzle cross-section, including the depth and radial directions. For the observation experiment, a glass capillary was used instead of an inkjet head nozzle, and a model ink was used instead of a water-based pigment ink. Three types of glass capillaries with different inner diameters were used to compare the effects of evaporation rate. For the model ink, a colloidal solution of silica particles dispersed in a mixture of water and glycerol was prepared. The observation results showed that the particle diffusion coefficient tended to decrease and become more distributed with decreasing inner diameter in the depth direction of the glass capillary. On the other hand, in the radial direction, there was almost no deviation in the particle diffusion coefficient for any inner diameter of the glass capillary, indicating that under the present conditions, thickening progressed in a diffusion-dominated manner.