Technological watch

Three bubbles for blown shrink film

Kuhne Anlagenbau focus at NPE 2024, Orlando, Florida, USA, 6-10 April, will be on large turnkey lines for extruding flexible simultaneously biaxially oriented barrier shrink films that do not require polyamide or polyester 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 microns, 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 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 Anlagenbau 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 microns for lid films and 50 microns 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 1,500 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.

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).

Publication date: 17/04/2024


This project has been co-funded with the support of the LIFE financial instrument of the European Union [LIFE17 ENV/ES/000438] Life programme

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Last update: 2022-01-31