Electrostatic Printing Assist (ESA)
Why does gravure printing actually need electrostatic printing assist systems?
Until a few years ago, electrostatic printing assist systems were some kind of “face-lift“ for publication printing. In most publication printing presses, electrostatic printing assist systems are now a matter of course, because they provide a substantial improvement in ink transfer, even at high printing speeds. “Missing dots“ are thus a thing of the past. The final product is a higher-quality printed image having high ink and colour density.
The primary issue
At first glance, the paper surface appears to be smooth. But, if you look at it through a microscope, you will see that it has a rough surface. In the nip, this irregular “fibre jungle“ is faced with 4,900 cells per square centimetre. All of those cells are expected to transfer their ink content to the paper within a split second. Thus, at normal printing speeds, mechanical contact alone does not always result in complete ink transfer from cells to paper. This phenomenon worsens at higher printing speeds and at printing of coated or other pre-impregnated substrates.
The electric field generated by the ESA in the printing nip causes the ink to be pulled completely out of the cells and transferred onto the substrate.
The results: YInk transfer to the paper or the film surface with point accuracy – without excessive impression roller pressure.