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Improving Processes for High-PCR Blown Film

RKW and Nordson enable film producers to process blown film with high recycled content.

Posted by Staff

October 24, 2023

5 Min Read
continuous screen-cleaning system
Thomas Steffen (RKW), Sven Pastrik (RKW), and Stefan Wöstmann (Nordson) with the continuous screen-cleaning system for blown film.Image courtesy of Nordson

Improving sustainability for plastic products and packaging is reinforced by national, state, and local governments through new laws, regulations, and charges. In Europe, virgin material used in packaging products will be subject to country-specific fees ranging from €0.23 to 0.45 per kilogram of packaging material. These changes in EU packaging laws are aimed at promoting the circular economy in the plastics industry.

The new regulations are a significant hurdle for film producers that must rapidly modify their film production to accommodate a large volume of recyclable materials.

However, this challenge can be advantageous for those who are well-prepared. At RKW in Echte, Germany, the use of recyclable materials has been a topic of discussion for quite some time.

"We have been using recyclables in our films for many years," explains Thomas Steffen, an application engineer at RKW. "These films are subsequently used in products where quality standards can be met through recycled material."

Efficient filtration is crucial to maintain the quality of the finished product when using post-consumer-content recyclate (PCR). Melt filters have been utilized in blown film lines for many years, but in the past these filters were mostly discontinuous, requiring the line to shut down for a screen change.

"In processes with clean virgin material, this is not a problem," says Stefan Wöstmann, process engineer at Nordson BKG. "The filters take on a purely protective function and ensure that no loose screws from the material feed or other transport contaminants get into the process. But the degree of contamination is so low that screen changes are rarely necessary."

Compensating for PCR quality differences.

The process needs to handle an additional component with much impact on the final product when using recycled material because the amount of dirt particles fluctuates significantly.

“Thus, we cannot guarantee that the quality of the final product is always the same. We needed to enable ourselves to react flexibly to varying levels of contamination,” says Sven Pastrik, manager of extrusion at RKW in Echte.

As a first step, continuous screen changers were implemented, which 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 significantly," reports Pastrik. "We can compensate quality differences in the material very well and process high proportions of recyclate, for example, in our form-fill-seal (FFS) bag production."

Recyclate is increasingly used in RKW's ProVent plastic bags.

The use of recyclate in RKW ProVent plastic bags, commonly used in the construction and chemical industry for packaging powdery goods, is increasing.

“It is essential that the protective and barrier properties are guaranteed and that no dust, dirt, or moisture can penetrate," explains Steffen. "We inspect our films with optical systems before further processing. For us, finding defects is not a strategy; the goal is to prevent them altogether. We knew that the proportion of recycled material would keep increasing and that we would have to redefine the filtration process when designing a new five-layer line."

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,” Steffen says. “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 Pastrik.

Development continues, according to Wöstmann. "The EU's Green Deal and national packaging laws are massively increasing the pressure and forcing system and component manufacturers to act."

PCR processing solution: Innovative backflush screen changer from W&H.

To expand the application window and process higher proportions of recyclate and prospectively even highly contaminated materials without compromising quality, a screen changer with backflush function was used.

"Melt filters without a backflush function reach their limits when processing recycled material,” Wöstmann points out. "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 changes in temperature, viscosity, and pressure, 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 de-aeration 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 recycling filter. It’s specially designed for blown film lines and has a compact design suitable for tight spaces.

Maintaining constant pressure is crucial for a successful operation of a blown film line. 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," notes Wöstmann. "The BKG HiCon K-SWE-HD/RS is equipped with a 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. Filling is so sensitive that no air pockets endanger the process or the finished product.”

The start-up was a complete and immediate success.

"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.”

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