Traitement d'un film soufflé à haute teneur en matières recyclées
RKW et Nordson prennent des mesures pour préparer l'avenir en permettant aux producteurs de traiter des films soufflés à haute teneur en matières recyclées
La durabilité devient de plus en plus importante pour les produits en plastique, et ce message a été renforcé par l'UE et les gouvernements des États à travers de nouvelles lois, réglementations et taxes. Les matériaux vierges utilisés dans les produits d'emballage seront soumis à des frais spécifiques à chaque pays allant de 0,23 à 0,45 euros par kilogramme de matériau d'emballage. Ces modifications de la législation européenne sur l'emballage visent à promouvoir l'économie circulaire dans l'industrie du plastique.
Les nouvelles réglementations constituent un obstacle important pour les producteurs de films. Ils doivent rapidement modifier leur production de films pour accueillir un grand volume de matières recyclables.
Cependant, ce défi peut être avantageux pour ceux qui sont bien préparés. Chez RKW à Echte (Allemagne), l'utilisation de matériaux recyclables est un sujet de discussion depuis longtemps. "Nous utilisons des matières recyclables dans nos films depuis de nombreuses années", explique Thomas Steffen, ingénieur d'application chez RKW. "Ces films sont ensuite utilisés dans des produits où les normes de qualité peuvent être respectées grâce à des matériaux recyclés. »
Une filtration efficace est cruciale lors de l'utilisation de produits recyclés pour maintenir la qualité du produit final. Les filtres à fusion sont utilisés dans les lignes de film soufflé depuis de nombreuses années, mais dans le passé, ces filtres étaient pour la plupart discontinus, ce qui nécessitait l'arrêt de la ligne pendant un changement de filtre. "Dans les processus avec des matériaux vierges propres, cela ne pose pas de problème", déclare Stefan Wöstmann, ingénieur de processus chez Nordson BKG, "les filtres remplissent ici une fonction purement protectrice et garantissent qu'aucune vis desserrée de l'alimentation en matériaux ou d'autres contaminants de transport ne pénètre dans le processus. Mais le degré de contamination est si faible que des changements de dépistage sont rarement nécessaires. »
Compensation des différences de qualité des matériaux
En utilisant davantage de matériaux recyclés, le processus doit gérer un composant supplémentaire ayant un impact important sur le produit final. "La qualité du produit recyclé en ce qui concerne les particules de saleté qu'il contient varie considérablement.As a first step, continuous screen changers were implemented. These filters allow operators to change screens without interrupting production and adjust screen fineness for different production batches based on quality requirements. "As a result, we have significantly fewer machine downtimes, and the productivity of our plants has increased distinctively," reports Sven Pastrik. "We can compensate quality differences in the material very well and process high proportions of recyclate, for example, in our FFS bag production."
Thomas Steffen (RKW), Sven Pastrik (RKW), Stefan Wöstmann (Nordson BKG GmbH) presenting a Nordson® BKG® NorCon™ K-SWE continuous screen changer in a blown film line at RKW.
The goal was a system in which high-quality films could be produced in a continuous, automated process. "We needed a plant concept with fast setup and changeover times. We don't want to deal with screen changes and thus line downtimes often and for a long time, but rather ensure an extrusion process that is as uninterrupted as possible."
RKW had a positive experience with Nordson® BKG® screen changers, leading them to approach the filter manufacturer again. Their new five-layer plant is now equipped with continuous BKG® screen changers and has been running successfully since 2021. "We are very satisfied with the performance of the system. Thanks to continuous filtration, we produce high-quality films with high recycled content in an uninterrupted process and can cover a wide application window," explains Sven Pastrik.
At RKW and Nordson, they were certain that the development must go further. "The use of recyclate will continue to increase in the future," explains Stefan Wöstmann. "The EU's Green Deal and national packaging laws are massively increasing the pressure and forcing system- and component manufacturers to act."
Stefan Wöstmann (Nordson BKG GmbH) and Sven Pastrik (RKW) with the new Nordson BKG HiCon K-SWE-HD/RS recycling filter.
The Solution: An Innovative Backflush Screen Changer
To expand the application window and process higher proportions of recyclate and prospectively even highly contaminated materials, e.g., from the yellow bag, without compromising quality, a screen changer with backflush function has now come into play. "We are already seeing that the backflush technology enables the use of recyclate from the PCR area," explains Sven Pastrik."At RKW and Nordson, they were certain that the development must go further. "The use of recyclate will continue to increase in the future," explains Stefan Wöstmann. "The EU's Green Deal and national packaging laws are massively increasing the pressure and forcing system- and component manufacturers to act."
"Melt filters without a backflush function reach their limits when processing recycled material. The degree of contamination is high, and the screens become clogged quickly," explains Stefan Wöstmann. "Screens are expensive, and changing them is time-consuming. Backflushing repeatedly clears the screens of contaminants and deposits, so manufacturers need fewer filter elements, and operators have to change screens less often."
It was necessary to adjust to the conditions to achieve optimal results in blown film lines. Since the film bubble is sensitive to temperature, viscosity, and pressure changes, even minor deviations can negatively impact the final product. Adding recyclates to the process can make it even more challenging. Pressure fluctuations during screen changes, backflushing, and deaeration can significantly reduce film quality or cause downtime. To address this issue, Nordson collaborated with equipment manufacturer Windmöller & Hölscher to develop the Nordson® BKG® HiCon™ K-SWE-HD/RS backflush screen changer. This new filter is specially designed for blown film lines and has a compact design suitable for tight spaces.
Eliminating Even the Slightest Pressure Fluctuations
Maintaining constant pressure is crucial for successfully operating a blown film line. Any material withdrawal for screen changes or backflushing can result in a balancing act in this area of tension. Hence, it is imperative to avoid pressure fluctuations through intelligent solutions in the high-pressure range. Each screen change in the filtration process is a sensitive step since the empty cavity must be refilled with melt after the change. If this is done too quickly, it can lead to pressure fluctuations and quality issues. "This is a major problem with blown film lines, as the film is usually very thin and sensitive to such changes," explains Stefan Wöstmann. "The BKG HiCon K-SWE-HD/RS is equipped with the patented melt pressure-controlled venting start, which fully automates the filling of the screen cavity after the screen change and thus ensures maximum pressure consistency. In addition, filling is so sensitive that no air pockets endanger the process or the end product. Manufacturers can rely on a stable process and high blown film quality."The new BKG HiCon K-SWE-HD/RS was provided to RKW as part of a user test and installed in a 3-layer plant. "The start-up was a complete success. We installed the screen changer and produced film successfully immediately; our machine operators were thrilled," reports Sven Pastrik. "The handling of the screen changer is simple, and due to the high degree of automation, we only have to intervene minimally in the process," explains Detlef Nolte, machine operator. "The fact that a newly developed machine was installed in one of our lines without any complications and then works so well directly is quite remarkable. In addition, it is immediately apparent that the experience gained from the initial joint project has been directly incorporated into the new screen changer.”
Meeting Future Challenges
RKW and Nordson plan to continue working together long-term to meet future challenges. "The shift from virgin material only to recycled material is huge. With the BKG HiCon K-SWE-HD/RS, we offer blown film producers an efficient tool to achieve this goal, says Christian Schröder, Global Segment Manager Recycling at Nordson. "With this machine, we are helping to make plastic packaging more sustainable. We are proud of that."RKW also made a strong commitment to sustainability. Recycling is considered a crucial component of this commitment. Each site has recycling facilities that process internal and external production waste into high-quality recyclate. The company is dedicated to investing in new technologies to further this effort. Sven Pastrik explains, "Our goal is to increase the proportion of recycled material used, depending on the specification, and also incorporate PCR material. We are fortunate to have filtration experts on our team to help achieve this goal."