Investigation on electrostatic assist and gravure process parameters on solid mottle reduction for shrink films
Akshay V. Joshi, Christoph Dettke & Joseph Steingraeber
Gravure is a high throughput printing process, normally associated with speed, quality, and long print runs. It is widely used for printing on shrink films and other substrates. The shrink films, in particular, polyvinyl chloride (PVC) and glycol-modified polyethylene terephthalate (PET-G), are two dominant substrates widely consumed and printed by gravure process. The PVC and PET-G offer different properties which greatly influence the printability. The surface energy of the substrate determines the adhesion and wettability of ink, while electrical properties such as surface and volume resistivity impact electrostatic assist (ESA) performance. The introduction of ESA in gravure further improved the print quality by eliminating dot skips with reduced impression pressure. However, print defects such as print mottle is inevitable. Print mottle occurs due to a discrepancy between substrate, ink, and process parameters which degrade the print quality. These complexities need to be addressed to deliver higher productivity with less print waste. Therefore, the study investigates the effect of process parameters, i.e., substrate type, line screen, air gap (distance between charge bar and impression roller), viscosity, voltage, and speed, and aims to quantify their effect numerically on defect minimization. The Design of Experiments (DOE) was generated for the above-mentioned parameters and analyzed to extract the best combination of process parameters. The optimized setting showed a reduction in solid mottle by 54% and 57% for PET-G and PVC, respectively.
ESA- a reliable technology not just for gravure package printing
By Ansgar Wessendorf
For many years, Enulec of Germany has specialized in the production of electrostatic print assist systems (ESA) Jor gravure printing applications. However, package printing, with its extensive use of widely differing film substrates, is still a particular challenge for the reliable application of ESA systems.[…] The Enulec ESA RotoFilm satisfies the specific requirements of the packaging printing market. The main feature of the top-loading system is a virtually maintenancefree, air assisted charging bar. lt also offers a reduced gap between charging bar and impression roller and sufficient electrostatic assist even at low speeds.Another feature of ENULEC ESA systems is “Balances Charging”. This patent pending process balances the charges on the impression rollers in gravure presses, which in turn significantly reduces the charging of the films. However, the use of this system also increases reliability when printing paper and cardboard substrates, and several European gravure press manufacturers have confirmed its effectiveness. […]
Published in Gravure Global Edition 2021
From a garage to a leading supplier of eledrostatic assist equipment
Everybody knows the success story of Microsoft, starting as a garage start up and developing into a world company, which fundamentally changed the world of communication. Not that spectacular is the story of Enulec, but the company also started in a garage and eventually became a worldwide leading supplier of electrostatic assist equipment, which improves ink transfer from the gravure cells onto the substrate, and thereby avoids missing dots. Hubertus Dettke, who studied electronic engineering and made an internship with the Swiss ESA supplier Spengler, founded Enulec (Energieübertragungselektronik – energy transfer electronics) still as a student together with his wife Christa, and they actually began with their activities in the garage of their private house.
Now, thirty-six years after its founding, Enulec’s modern premises and headquarters are located in Trittau, not far away from the north German harbour city of Hamburg. Over thirty highly qualified engineers and technicians are employed here to develop and manufacture ESA equipment for the packaging, decorative and publication printing industries. There are subsidiaries in Lugano, Switzerland and in St. Louis, USA, as weil as service centres and trade partners around the globe to support their worldwide customers. Altogether more than 7500 ESA installations from Enulec are now in operation all over the world. […]
Published in Gravure News 182/18
Gravure printing without missing dots
By Ansgar Wessendorf
Electrostatic printing assist (ESA) generally improves print quality, since it helps to eliminate missing dots. But if the press operator has selected the wrong ESA system or uses it incorrectly, it can itself cause problems with gravure printing presses.
On modern gravure printing press-es for decor and flexible packaging, ESA is standard equipment. ESA is decisive in ensuring that the ink is transferred from the cells of the gra-vure cylinder to the substrate, thus improving the quality of the print itself. However, setting and operat-ing the ESA improperly can lead to problems in the print run. Select-ing the right system and observing a few basic rules can prevent such problems arising.
Charging the impression roller with an electrostatic charge generates an electrostatic static field between the impression roller itself and the grounded gravure cylinder which exerts a force on the ink in the cylinder´s cells. This force en-sures that nearly all the ink in the cells is transferred to the substrate. In this way, ESA systems supports a proper print.
The ESA principle is based on the fact that an electrostatic charge is drawn towards an opposed charge surface until equilibrium is achieved. The ink has the same neu-tral charge as the gravure cylin-der, while the substrate is positively charged. Electrostatically charging the impression roller changes the surface tension of the ink in the cells of the gravure cylinder, the closer the ink approaches the web. The ink is pushed upwards along the walls of the cells by the electrostatic force. It is polarised in the cells and extends itself, so that the only way out is up, until it comes into contact with the substrate. […]
Published in Flexo & Gravure Global 2-2014
Advancements in ESA in Rotogravure
By Joseph K. Steingraeber
Electrostatic Printing Assist (ESA) has contributed more to improve the quality of rotogravure printing than any other innovation. ESA systems optimize ink transfer from the gravure cylinder to the printing substrate. Over the past 30 years ESA power supplies and application mechanisms have undergone many changes. Such technical developments, particularly those from ENULEC, have since raised the bar for ESA. […]
ENULEC designs and builds only capacitance-free high voltage generators having high internal resistance that enable optimum power transfer to the ESA impression roller and increases the performance of the ESA system considerably. With capacitance free technology, the ESA charge bars can be guaranteed safe and current-free immediately after the system is switched off as there is no residual charge in the system. Alternatively, when the ESA is switched on, high voltage is available immediately and the system can be used straight away without delay. This specially developed capacitance-free high voltage generator enables the system to be used in conjunction with ESA impression rollers having high surface resistances, including resistances outside the range normally specified. This results in a substantial increase in impression roller life related to electrical specification…
Published in GRAVURE/ Summer 2012
Slowly and steadily
This year Enulec is celebrating its 30th anniversary and is enjoying greater success than ever before
When a small family company like Enulec is able to perform with such great success on the world market stage for three decades, a fundamental question inevitably needs to be answered: What is the secret of this success? In Enulec’s case, there are two main factors which have contributed to their success. Firstly, it is concentration on a manageable range of high-quality products, designed to meet the needs of the market and continuously developed over the years; and, secondly, Enulec has a closely knit global network of partner companies with which close and intimate relationships have been built, often over long periods of time. These support the Trittau-based company, located close to Hamburg/D, not only in matters of service and support for their international customer base but also in the further development of their innovative products. One such product is the »air-assisted charge bar«, an Enulec innovation, protected by a registered design in Germany, which has set new standards in the gravure printing industry. And to top all of this, Enulec has recorded the highest intake of orders ever in its history during the first five months of 2011, its 30th anniversary year…
Published in FLEXO & GRAVURE ASIA 2-2011