Triple Bubble Technology for soft, recyclable barrier shrink bags

2024-05-30

At the NPE 2024 fair in Orlando (United States), Kuhne Anlagenbau GmbH stood out for its large turnkey lines for the extrusion of soft barrier shrink films with simultaneous biaxial orientation, which do not need to contain polyamide (PA) or polyester ( PET) as a reinforcing layer in the structure. This means that they can be easily recycled along with (a maximum of 5% of) EVOH in the PE recycling stream. The films acquire the required robustness and puncture resistance while being processed in-line in the Triple-Bubble process thanks to the use of soft beam cross-linking performed by Kuhne. Such cross-linking acts from the outside to a depth of only 5 to 10 µm without damaging the EVOH layer or reducing the recyclability. In this way, a work phase that would be later and would increase the costs of the procedure is eliminated. The films obtained are soft and elastic enough to achieve high shrinkage values. In addition, they offer the mechanical strength necessary to reliably fill the bags, even with goods weighing several kilograms.

Kuhne’s medium-sized Triple-Bubble blown film lines achieve throughputs of up to 250 kg/h in the production of soft, recyclable barrier shrink bag films. © Kuhne Anlagenbau

Kuhne supplies the technology used in the form of complete turnkey lines for use throughout the world. This comprehensive package is tailored to the requirements of each product and also includes the specification of the required material formulations and thicknesses for the seven to thirteen PE, adhesion promoting and EVOH layers, as well as all processing parameters. In this way, Kuhne can usually commission these lines within a very short time after assembly, so that a high level of quality in continuous production can be maintained from the beginning. Recyclable films help the manufacturer and distributor reduce Extended Producer Responsibility (EPR) rates and support compliance with the CEFLEX (Circular Economy for Flexible Packaging) sustainability guidelines formulated by the sector. Kuhne lines stand out compared to the competition, since, taking into account the performance in relation to the costs of the machine in production conditions, the investment costs are significantly lower.

The refinement of the Triple Bubble process, which was developed in-house by Kuhne Anlagenbau in 1996, allows the processor to benefit from the attractive combination of low film thicknesses and high performances achieved with large machines. Typical film thicknesses range from 20 µm for lid films to 50 µm for shrink bags, saving on material. In this regard, a retraction of more than 60% can be achieved. Thanks to the optimized machine design and high cooling rates, the lines allow outputs of up to 250 kg/h or an annual production of more than 1,500 t of shrink bag film. Depending on the current requirements of different regions and applications, PVDC interlayers can be used instead of EVOH, as well as PA or PET outer layers, to increase puncture resistance.

Triple-Bubble® technology

Triple-Bubble technology for the production of bioaxially stretched blown films gets its name from the serial arrangement of three bubbles. In the first, the film is cooled very quickly with cold water using water cooling technology. Kuhne has further optimized this process to increase the efficiency of large lines. He very effectively prevents the formation of crystals, which is necessary for uniform stretching in the second stage. The high orientation achieved at the molecular level is the key to the excellent mechanical and barrier properties of the films. The thermal relaxation in the third bubble serves to establish the desired shrinkage behavior, so very low shrinkage forces can also be achieved.

Among the most common uses for barrier shrink films produced by Kuhne’s Triple-Bubble process are soft or rimmed portion packaging for meat and cheese. © Kuhne Anlagenbau

Today, Kuhne Triple-Bubble lines can produce shrink films of up to 13 layers with widths of up to 3,000 mm in double plane (6,000 mm film width). “Around the world, we have already delivered around 150 of our Triple-Bubble lines turnkey according to schedules and requirements. Thanks to the combination of line development and production, as well as on-site assembly, film formulation for specific applications and pre-optimized process parameters, commissioning the line is easy and the customer can directly start production reliably and without own development costs, even for difficult applications. The license to use the respective patents is included,” explains Jürgen Schiffmann, CEO of Kuhne Anlagenbau.