Adhesive-free roll change: electrostatic and contactless

The roll-to-roll process enables the coating, printing, or laminating of flexible substrates such as paper, films, or composites at high production speeds. The material is continuously unwound from one roll, processed, and wound onto another roll. Electrostatic turret winders have proven to be an efficient technology for optimizing the winding process, ensuring precise web guidance, enabling automatic non-stop roll change, and improving the quality of the end products.
Turret winders: principle of roll change
Fully automatic roll change on a reversing winder of a packaging printing machine is a high-precision process that takes place in several steps. It is usually triggered by a signal or an automatic control as soon as the printed roll has almost reached its maximum winding diameter. The printing machine prepares for this by regulating the speed and stabilizing the material web.
Once the roll is fully wound, a cutting device—such as a serrated cross-cut knife—separates the substrate web. This cut is usually made at right angles to the web to ensure a clean separation.

The reversing disc then rotates by approximately 180°, bringing the finished roll into the removal position and simultaneously moving a new core into the winding position. This ensures that the production process continues without interruption.
The substrate web—whether paper, film, or a composite material—is then guided onto the new core and fixed in place. Maximum precision and exact alignment are crucial to ensure consistent winding quality. Once the substrate web is correctly positioned, the winding process starts again. The printing machine dynamically adjusts the speed and tension to continue the winding process optimally.

The problem with cardboard cores

Cardboard cores are normally used as winding cores, which are fitted with special adhesive tapes or adhesive coatings to securely fix the start of the web. However, this method poses considerable challenges for the recycling process and disposal systems.
Cardboard cores covered with adhesive tape—especially plastic tape—are considered mixed materials. Since the various components cannot be completely separated, they must be recycled or disposed of using complex processes. Manual removal of the plastic component is often necessary, which causes additional work and costs.
In addition, adhesive residues often remain on the cardboard even after the adhesive tape has been removed. These residues impair the quality of the recycled paper and complicate the processing process because they are not biodegradable.

Another problem arises from the variety of substrates that need to be processed. Materials such as thin paper, metallized films, or thick substrates require different types of adhesive tape to ensure optimal adhesion. This not only means additional material costs, but also increased time and personnel costs for the correct selection and application of the adhesive tapes.
AST technology for contactless electrostatic roll change was developed by Enulec to enable automatic roll change on the reversing winder without the use of costly adhesive materials, without waste at the beginning and end of a roll, and without the risk of damaging the substrate web.
Thanks to this electrostatic concept, an adhesive-free roll can be produced that remains free of unwanted adhesive residues during further processing and can be unwound completely and without problems until the end. The gentle and uniform electrostatic forces minimize mechanical stress and reduce the risk of material damage. This is particularly advantageous for sensitive or thin materials such as coated paper or films.

How does the AST system work?

The Enulec AST system is positioned in the reversing winder so that the substrate web passes through the effective range of the charging electrode, which generates consistent charge intensities at a defined distance. This allows the system to be flexibly integrated into various types of machines and production areas.
The arrangement of the charging electrode at a defined distance from the web also allows for a certain tolerance to changes in web travel, for example due to the increase in roll diameter during the winding process onto the winding core.
A film is fixed against a ground potential, such as a steel core, by generating an electric field. The interaction between electrical forces and gravity has a stabilizing effect on the film.
Different materials have different electrostatic properties. While some can be easily electrically charged, others are less sensitive to electrostatic forces. Typical substrates include plastic and composite films that contain plastics. In composite films, these plastics can be present in various forms—as a separate film, as an extruded layer, or as incorporated plastic particles.

In addition, composite films may contain other layers such as metal foils, paper, cardboard, or additional plastic films. In many cases, they combine several of these material layers to achieve specific material properties.
Even paper can be charged by a strong electric field generated by a high-voltage source. Since processing usually takes place under controlled conditions, factors such as material properties and humidity can prevent the paper from immediately dissipating the resulting charge fluctuations.
Enulec inline measurement records the charge on the substrate web resulting from previous processing (e.g., extrusion). The measured data is transmitted to the Enulec control device, which determines the optimum voltage level and polarity based on the field strength and material-dependent variables. This is then transferred to the substrate via the AST charging electrode to ensure safe and precise fixation to the winding core.

Charging electrode with air support

After successful winding, charging is deactivated and, if necessary, discharging is activated. This application can be implemented with both Enulec standard charging electrodes and the low-maintenance Enulec ESA1000 charging electrode with air support, which effectively prevents contamination.
This specially developed Enulec charging electrode eliminates the need for cleaning intervals, thereby reducing maintenance costs. A slight overpressure at the needle tips ensures that contamination does not foul the needles. The unique design, in which each individual ionization needle is positioned in its own air-flow channel, ensures consistently high charging quality at all times.
The electrostatic AST charging system is controlled via an industrial touch screen or a single control module. The touch screen displays the units and relevant parameters, which are also managed in the Roto-Green quality management system developed by Enulec.

Integration and control with Roto-Green Control

The AST charging system is controlled either via an industrial touch screen or a single control module. The touch screen displays the units and relevant parameters, which are also managed by the Roto-Green quality management system developed by Enulec.
The in-house Roto-Green Control software forms the backbone of Enulec technology. It not only provides information on changes in electrical resistance, but also retrieves stored work profiles that enable automatic adjustment to achieve the best possible performance. As the basic operating system, it controls all Enulec applications, recording, evaluating, and managing all relevant data.
Modern electrostatic reversing winders are often equipped with advanced control systems that monitor the entire winding process. Sensors measure the tension of the material web and the speed of the winding process, allowing the printing machine to make automatic adjustments to ensure consistent quality and efficiency. In addition to the Enulec touch screen, machine-internal controls can also be used to control the AST system.

Digitalization requires the connection of machines, tools, and IT systems, linking and making available all data that is important to the company. The Roto-Green Control System not only controls the components of the in-house Enulec technology, but also serves as a gateway that enables communication between internal and external networks—an indispensable link for modern printing press and production plant control.

Track record and advantages

The AST system is successfully used in reel-to-reel winders for web-fed printing presses, including gravure, flexographic, and offset printing presses. It is also used in all areas where web material made of electrically insulating material is wound onto a roll. This includes laminating machines, extrusion film lines, and, most recently, slitters.

In 2023, a development project was launched in collaboration with a leading European packaging manufacturer to test the processing of 28 composite materials in various thicknesses and widths.
Even in standard runs, the Enulec AST electrostatic winding technology achieved an impressive 90% success rate. While curling effects occurred with certain materials, the project was able to achieve a 100% success rate by adding compressed air. This success underscores how eliminating adhesive sleeves enables comprehensive process optimization.

The key advantages include:

• 100% single-variety disposal of residual film and cores, which makes a significant contribution to sustainable production and at the same time leads to a significant reduction in costs
• Reduction in production waste: substrate webs can be used up to 100% because the substrate rolls can be unwound down to the core. This means that there is virtually no waste from scrap, which also leads to considerable cost savings.
• Improved work ergonomics, higher employee satisfaction, and a general increase in productivity

Conclusion

Electrostatic turner winders reduce material losses and production downtime, making production more cost-efficient. They require less manual intervention and additional troubleshooting systems. Their high efficiency increases production capacity. In times of resource- and environmentally-friendly production, the Enulec AST system contributes significantly to greater efficiency, safety, and cost reduction.