A novel method to study the effect of corona treatment on ink wetting and sorption behavior

Abstract

A novel absorption test method was developed based on a modification of the Bristow Absorption Apparatus. The proposed method combines corona treatment (CT) with short contact time absorption behavior to study particularly ink wetting and sorption on substrates in-line. The method makes it possible to study e.g. the coagulation of pigment inks induced by deposited charges i.e. electrocoagulation, the effect of short contact times on liquid/substrate interactions, and problems related to charge decay such as whiskering. In-line measurement with a short delay time minimizes the effect of ambient conditions (heat, moisture) on charge decay, and thus simulates the conditions in commercial digital printing processes. The functionality of the method was evaluated by testing paper samples with and without polymer coatings. Uncoated samples were used to study absorption properties. It was found that in some cases the CT changes both the wetting and absorption of ink and that in other cases the main changes are in the absorption behavior. Four CT levels (0, -100, -450, and -900 W*min/m2) were studied and it was found that the highest treatment level increased the absorption of the applied inkjet ink the most. As expected, the contact time between liquid and substrate was found to be an important variable affecting the absorption. Print density and mottle were determined on coated samples with the CT levels of 0, -160, and +160 W*min/m2. CT improved print density significantly, whether the treatment was positive or negative, and also reduced the mottling tendency.