A novel approach for studying the effects of corona treatment on ink-substrate interactions

A novel method combining corona treatment and Bristow's wheel has been developed to study the effect of corona charging on immediate liquid-substrate interactions. The assembly makes it possible to study the effects of in-line corona treatment, where the delay between the charging and the application of ink is very short but is adjustable from milliseconds to hours or days. The short delay between these process phases is a prerequisite when studying and interpreting liquid wetting and sorption phenomena on substrates, because polar species and polarization effects formed during corona treatment may be both short and long-lived and the influence of short-lived effects on immediate liquid-substrate interactions can be significant. The study focuses on evaluating the effects of direct current corona treatment on inkjet ink absorption mechanisms and printability. The substrates were fine papers surface-treated with cationic polydiallyldimethylammonium chloride, anionic sodium carboxymethyl cellulose and anionic fumed silica-based formulations. Both positive and negative direct current corona treatments were studied and it was found that corona treatment increased the optical density of the ink layer and reduced the mottling of ink tracks, indicating a change in the ink setting process. As expected, contact time was an important variable affecting the ink absorption behavior and the visual quality of the ink track. The absorption-normalized density values revealed significant differences between the substrates.