Ink lifting efficiency from engraved cells under electric field

We endeavour to clarify the effect of electric field on speed and height of ink lifting from differently engraved gravure cells. The main emphasis is directed to the shape of the cell, whether it has sloped or vertical walls. Furthermore, the influence of ink and substrate properties as well as patterns and defects in the substrate on electric field assisted ink lifting was studied. An extensive set of numerical simulations was carried out and the results were verified by experimental studies. A model was developed to illustrate ink movements in a cell approaching the nip. Laboratory arrangements were set up to image electric field assisted ink lifting from the side using scaled-up V- and U-shaped grooves. Transparent impression roller arrangements were used to monitor ink lifting and formation of ink-substrate contact using electromechanically engraved and laser etched gravure cylinders. According to our simulations and experiments, ink first moves towards the front edge of the cell where the effect of the electric field is the strongest. As the influence of the electric field at the trailing edge of the cell increases the ink is also lifted from that side and an ink meniscus is formed inside the cell. The transparent impression roller images proved the forming of an ink meniscus inside the cell thus predicting printed doughnut dots. Based on the simulations, a void on the substrate has an influence on ink lifting depending on position of the void relative to the front edge of the cell. This could be one explanation to missing dots. The model provides excellent possibilities to study the influence of the process parameters on ink lifting and, in general, liquid movements in electric field. The laboratory arrangements can be utilized in different gravure applications especially when compatibility of materials or the influence of electric field is studied.