Comparison of different experimental methods for measuring droplet size in inkjet printing

Abstract

In the inkjet printing process, controlling the droplet size is essential to ensure uniform thin film, a critical factor for achieving high performance of electronic devices. In this study, we evaluate the accuracy and applicability of three droplet measurement methods using inks with different properties. The first method is the laser diffraction method, which measures individual droplets based on the Fraunhofer diffraction in real time. The second is the mass measurement method, which calculates the droplet mass using a microbalance and employs evaporation compensation to minimize evaporation effects, and the third method is the shadow imaging method, a widely adopted commercial technique based on the international standard. To evaluate the accuracy of these measurement methods with three inks having various boiling points (BP), laser diffraction serves as a benchmark here to compare the results of the shadow image and mass measurement methods. Laser diffraction was selected because it shows better coefficient of variation about 1.7 % than the coefficient of variation of mass measurement and shadow imaging methods about 8.7 % and 6.4 %, respectively. The BP of the ink and measurement precision based on laser diffraction results were proportional to each other. These insights guide the selection of optimal measurement method for inkjet printing applications with printed electronic inks. When printed electronic inks with various boiling points were used, the laser diffraction method consistently demonstrated better measurement errors in droplet size than the mass measurement and the shadow imaging method.