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Triple Bubble® Technology for Recyclable, Flexible Barrier Shrink Bags

Kuhne Anlagenbau GmbH’s focus at NPE 2024, in Orlando, Florida, USA will be on large turnkey lines for extruding flexible simultaneously biaxially oriented barrier shrink films that do not require polyamide (PA) or polyester (PET) as a layer to impart strength to the structure. Consequently, they can be easily recycled together with (at most 5%) EVOH in the PE recycling stream. The required robustness and puncture resistance are achieved inline during processing in the Triple-Bubble® process using gentle radiation crosslinking employed by Kuhne. This acts from the outside to a shallow depth of only 5 to 10 µm, without damaging the EVOH layer and reducing recyclability. As a result, there is no need for an additional post-processing step, which would increase costs. The resultant films are sufficiently flexible and elastic to achieve good levels of shrinkage. At the same time, however, they also provide the mechanical strength required to be able to reliably fill the bags, even with contents weighing several kilograms.

Kuhne’s medium-sized Triple Bubble® blown film lines can achieve throughputs up to 250 kg/h when producing films for recyclable, flexible barrier shrink bags.  © Kuhne Anlagenbau
Kuhne’s medium-sized Triple Bubble® blown film lines can achieve throughputs up to 250 kg/h when producing films for recyclable, flexible barrier shrink bags. © Kuhne Anlagenbau

One-stop Shop

Kuhne supplies the entire technology used for this as turnkey lines for worldwide use. Tailored to particular product requirements, this one-stop package also includes the specification of the material formulations and gauges required for the seven to thirteen PE, adhesion promoter and EVOH layers, as well as all processing parameters. As a result, these systems can usually be commissioned very shortly after installation by Kuhne, and continuous production at the highest quality level is possible right from the outset. For manufacturers and distributors, the recyclable films mean lower extended producer responsibility (EPR) levies and assist compliance with the Circular Economy for Flexible Packaging (CEFLEX) sustainability guidelines drawn up by the flexible packaging value chain. Kuhne’s lines stand out from the competition because capital costs are significantly lower when output is considered in relation to machinery costs under manufacturing conditions.

Kuhne Anlagenbau, which developed the Triple Bubble® process in-house back in 1996, has perfected the system and can offer processors access to the attractive combination of low film thicknesses with the high throughputs achievable with large-scale machinery. Thus, typical film thicknesses are material saving, ranging between 20 µm for lid films and 50 µm for shrink bags. A shrinkage of over 60 % is achievable. Optimized machine design and high cooling rates mean the lines can achieve throughputs of up to 250 kg/h or annual output exceeding 1500 metric tons of shrink bag film. Depending on current requirements in different regions and applications, intermediate layers made of PVDC instead of EVOH, as well as PA or PET outer layers to increase puncture resistance are possible.

Triple Bubble® Technology

The Triple Bubble® technology for manufacturing biaxially oriented blown films is named after the serial arrangement of three bubbles. In the first, the film is very quickly cooled using cold water quench technology. Kuhne has further optimized this process for large systems to increase efficiency. This quenching very effectively prevents crystallization processes, as is essential for uniform stretching in the subsequent, second stage. The resultant high degree of orientation at a molecular level is key to the films’ excellent mechanical and barrier properties. Thermal relaxation in the third bubble is used to set the desired shrinkage behavior, so also making it possible to achieve very low shrinkage forces.

Kuhne’s current Triple Bubble® lines enable the production of shrink films with up to 13 layers at widths of up to 3000 mm double flat (6,000 mm film width). As Jürgen Schiffmann, Kuhne Anlagenbau’s CEO, explains, “We have already delivered some 150 of our turnkey Triple Bubble® lines worldwide on time and according to requirements. Our combination of system development and production together with on-site installation, application-specific film formulation and pre-optimized process parameters make commissioning the line straightforward, and customers can start production immediately - reliably and without in-house development costs, even for challenging applications. Patented technology licenses are included.”

Models of implemented large-scale lines will allow visitors to Kuhne’s booth at NPE 2024 (West Building Level 2, Expo Hall – W7789) to familiarize themselves with Triple Bubble® technology.

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