| Summary: | 碩士 === 國立臺灣大學 === 化學工程學研究所 === 103 === In recent years, gravure offset printing has received great attention for its high throughput rate and fine quality for printed electronics. However, incomplete liquid transfer leads to defects, such as satellite dots or broken lines, which deteriorates the printing quality. To solve this problem, many researches focus on the effects of different physical properties on the printing quality of gravure printing process. In this thesis, we looked in to how viscoelasticity affects the liquid bridge formation and breakup process, which is crucial for the printing quality. To study the fundamental physics of liquid transfer phenomena in the printing process, viscoelastic fluid, PEO water solution, was transferred from both axisymmetric and non-axisymmetric cells to a flat PET plate.
From the experiment results, we observe that viscoelastic fluid cannot form a complete liquid sheet during the stretching process for non-axisymmetric line cell; instead, breaking in to multi-liquid bridges, which results in reducing the weight of liquid transferred. This phenomena is so called multi-liquid bridges, and is affected by the properties of the fluid, stretching velocity, cell geometry and so on. Besides, unpinned contact lines caused by die swell also results in the decrease of fidelity, which is quantified by a dimensionless parameter, quality indicator.
Both multi-liquid bridges and die swell effect decrease the printing quality, which is defined by the weight of liquid transferred and quality indicator in this thesis. Critical Wi (Wi**) and dimensionless group 〖(λτw/η)〗^* were found. Therefore, multi-liquid bridges and die swell effect can be avoid, on the other words, good printing quality is able to be achieved, as long as the operating Wi and 〖(λτw/η)〗^* are smaller than the critical values. To conclude, to reach good printing quality under high printing velocity, it is believed that reducing the relaxation time is the most effective way.
|
|---|
