Experimental investigations of the liquid transfer between two separating plates have been carried out, with the aim of increasing the ink transfer ratio in micro-gravure-offset printing. A sessile droplet is divided into two by moving one plate vertically with respect to a fixed plate. The surface contact angles of the sessile droplet on the two plates were of particular interest in this study because the volume ratio of the two droplets varies with the contact angles. Various methods for controlling the surface contact angle, including chemical treatment, plasma surface modification and electrowetting-on-dielectric were assessed. Image analysis of the droplets was carried out to estimate the surface contact angles and to measure the volumes of the droplets. The liquid transfer process and related phenomena, such as satellite droplet generation and the variation in the contact areas between the droplets and the plates, were observed. The experimental results help us to determine the optimal surface contact angles of the plate cylinder, blanket cylinder and substrate for micro-gravure-offset printing.
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