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 solution
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.
Ribbon Tracking
New standards with Ribbon Tracking
Electrostatic ribbon tracking eliminates problems in the folder, such as trim irregularities and dog ears by electrostatically interlocking (tracking) the ribbons before cross cutting. This allows higher speeds in the folder, clean blocking of the individual ribbons, and proper delivery.
Remoistening
Why do we need Remoistening?
In the heatset web offset process the inks are dried with hot air. This is rapidly followed by a reduction in the water content of the paper, leading to considerable problems in the following processes.
Quality advantages
- Eliminates buckling of perfect bound cross grain products
- Prevents fibre breaking
- No growing of pages
- No climate waves (waviness)
- Reduction of tension waves (fluting)
The solution Electrostatic remoistening increases the water content in the paper after drying, returning to the level required.
Discharging
Sheetfed Presses
At the Sheet Feeder
A combination of Ion Blowers and Discharge Bars in the feeder prevents double feeding and sheet rolling during feeding. With some coated papers additional discharging may be needed on the feed board to prevent sheet “cocking”.
In the Discharge
Installing discharging bars at the delivery improves sheet flow and stack quality, improving efficiency and aiding downstream processing. Renmar Plastics Machinery can provide static bars able to fit between the chains of the gripper bars.
Discharge systems for packaging and decorative gravure printing presses as a preliminary installation for future implementation of an Electrostatic Printing Assist system
