The Dual Task of Electrostatic Systems -Part 2
Part 1 of this series of articles (In Issue 92) mainly covered the negative aspects of electrostatics. In this part, the beneficial aspects of specifically applied electrostatic charging is described
When specifically applied, electrostatic charging is highly beneficial and increases production performance (through blocking or precise fixation) during the production process. Electrostatic charging offers real benefits in terms of quality and efficiency, such as:
– Higher production speed;
– Increased efficiency;
– Optimised quality;
– Reduced energy consumption;
– Lower costs;
– Smoother processes;
– Minimised failures, stops, and waste.
Charging systems consist of a high-voltage generator and charging electrodes. They are mainly applied to speed up and protect processes, where materials have to be firmly combined for a certain period of time. The Eltex high voltage generators KNH35, KNH65and KNH124 generate up to 100 kVin both positive and negative polarity.
Voltage differences of 200 kV may occur in the alternating electrical fields (+,–). It is also possible to generate charges with a polarity (+or –) against the ground potential. The high-voltage electrodes are highly loadable, and due to the optimised arrangement of the electrode tips, the distribution of charge and electrical fields has been significantly improved. In addition, current- limited tips avoid any increase in air ionisation and brush discharge.
Attractiveness through performance
Charging technology for process optimisation is used in many industries. This includes laminating and coating (adhering or fixation of films), in-mould labelling (fixation of labels in the tool), and film extrusion (accurate, limited or continuous electrostatic fixing of films during processing; firm powder tacking on foil surfaces; exact core winding without (neck-in) and telescoping at the winding unit) (Figure 1 and 2).
The attractiveness of the technology is mainly based on advantages like low power consumption, compact power adaptors, single electrode for all applications, high efficiency, interference resistance and economical pricing.
Electrostatic printing assistance
Packaging and decoration gravure printing are some of the most important fields of application for electrostatic printing assist systems (ESA). ESA technology is based on the principle of the plate-type capacitor. This means that a homogeneous electric field is generated between two plates, in which a dielectric is pulled to one side. ESA applies this principle at the printing nip – precisely at the point where the ink is transferred onto the web (Figure 3).
This principle of ESA supported ink transfer works evenly over the entire web width and operates reliably at both very slow and very high production speeds. The application of ESA technology results in accurate printing on cardboard, paper, and film without any missing dots. Eltex ESA systems for gravure printing are installed worldwide in more than 6000 printing units and the company cooperates with all the well known press manufacturers. Although the majority of new gravure lines are already equipped with ESA, there is also a strongly increasing tendency for retrofitting already installed presses. The GNN75 system (DC charge, no charging electrodes) especially enjoys growing popularity. In particular, systems with air assisted charging electrodes are replaced by Eltex systems.
A promising future
The beneficial aspects of specifically applied electrostatic charging are increasingly used in a growing number of industrial areas which is also due to the fact, that applied high-voltages and low currents in the mA-range elicit low energy costs. For continuous further development of the ESA technology, Eltex intensively cooperates with machinery manufacturers and research institutes.
ESA applied at the printing nip to improve ink transfer.