Precision in seven layers - motan conveying and dosing technology at Greiner Packaging GmbH

A 7‑layer compound foil is used for the coffee capsules. Its central layer consists of EVOH (ethylene vinyl alcohol co‑polymer). It forms the oxygen barrier and is embedded on both sides via adhesion promoter layers of recycling material (punching waste). Coloured polypropylene layers (homo‑polymer and co‑polymer) are additionally applied as cover layers.

motan and Greiner Packaging have developed a sustainable production concept

As the cups of the coffee capsules are produced from the compound foil by deep‑drawing and punching, more than 50 per cent of the film remains as a punched frame. As this quantity of waste could not have been disposed of logistically or economically due to the projected mass production, Greiner Packaging developed a concept for complete recycling of the punching waste during ongoing production together with the long‑term system partners, the German motan group, a manufacturer of peripheral systems, and Luger GmbH from Austria, as motan project planners and plant fitters and the extrusion technology supplier. For this purpose, the multi‑layer foil to be produced must be adapted in such a way that up to 60 per cent of it can consist of the regrind of the original foil.

Fig. 2: The 7‑layer barrier foil which comes out of the extrusion machine runs directly into a multi‑cavity deep‑drawing and punching machine. The remaining punched frame and any bad parts produced are then fed directly into a cutting mill (in the background at the end of the machine) and fed back into the production line from there.

The punched frame and waste parts are ejected directly from the deep-drawing machine and fed into a mill (Fig. 2). The regrind goes either into a storage silo or into BigBags and is fed from there to the extrusion plant, where it is made into a mixed polymer which provides the two main layers of the compound foil. Therefore, including the addition of new material, 70 per cent of the total material throughput of the projected conveying and dosing unit is provided by the recycling circuit. The comparatively small material throughputs of the additional four extruders represent the remaining 30 per cent. These four extruders are arranged on two levels around the central “regrind extruder”, which is on the base level. It is flanked by the extruders for the central barrier layer and the adhesion promoter layers. The extruders for the two top layers are “on the first floor”. The material traps for the extruders underneath are on the second floor (Figs. 3 to 5).

Fig. 3: A 5‑aggregate extruder is used to produce the 7‑layer barrier foil. The central extruder is responsible for 70 per cent of the foil in the form of the recycling percentage. It is flanked by the extruders for the barrier layer and the adhesion promoter layers. On a production level arranged above this, the extruders for the PP cover layers are arranged, which are connected to the feed block via vertical smelting lines (visible in the background).

Fig. 4: The 7‑layer foil machine is constructed in three functional levels on top of each other. On the lowest level (not visible here) there are three extruders (see Fig. 3), on level two there are two extruders for the cover layers, on the top level the dosing units to supply the extruders situated below.

Fig. 5: Central mixing station to supply the “regrind extruder”. In this, four material components come together (regrind from the silo or from the BigBag, stabiliser for the adhesion promoter and new PP material) which are added from the gravimetric dosing units on the third level.

Compared to the complex dosing and mixing technology, the design of the pipeline system is simple and direct, with fixed piping to each material trap. There is no coupling station or intermediate material drying.

Dosing precision lies in the detail

As mentioned above, most of the material throughput is from the regrind layers, which are supplied via gravimetric dosing units and a downstream mixing system due to possible fluctuations in the bulk density. Comment by Helmut Reckziegel, Head of Business Unit Capsules: “In this regard it is worth mentioning that the regrind fed back into the multi‑layer foil as filler material consists of the 7‑layer foil and is therefore composed of the five different viscosity materials which this contains. It was our joint objective to achieve stable mixing and flow properties for this 5‑material mixture. An unstable material composition, whether due to fluctuating bulk density or a change in material proportions, leads to reductions in quality of the extrudate, in particular when seven layers have to harmonise with each other. As we wanted to install a control option for this, we provided for the addition of virgin PP material to the regrind.

Therefore, the continual enrichment of the concentrations of the percentage of EVOH and of the adhesion promoter in the total foil, triggered by the return of the stamping grid, can be stabilised at 14 and 12 per cent respectively and consequently the melt flow index.” (Fig. 6)

Fig. 6: Factors of influence on the composition of the regrind fed back into the cycle.

A further concept detail is worth mentioning: due to the shortest possible return of the regrind, it does not cool down completely. A large part of the heat energy contained therein can thus be used for faster melting in the extruder, which leads to an improvement in the energy balance in view of a material throughput on the “regrind extruder” of approx. 500 kg/hr.

All other material percentages are added volumetrically as virgin material in constant quality. The throughput quantities for the barrier material and the adhesion promoter are a maximum of 60 kg/hr. The throughput of PP layers, which are additionally mixed with a white or brown colour master batch, is somewhat more, at approx. 110 kg/hr (see Fig.1).

Complete machine transparently operable via master production computer

All machine components are activated and operated via the remote‑controlled electronic modules specifically developed by motan for this purpose. These are GRAVInet for gravimetric dosing units and VOLUnet for volumetric dosing units. They are connected to a ControlNet of the central machine control via Ethernet or TCP/IP. This can be extended up to LINKnet, a comprehensive plant management system (Fig.7). It is thus possible with Linknet 2.0 to collect and log the process sequences and application data and to operate all connected controls up to device level. All motan controls with communication capability can be connected. Batch tracking is therefore continuously possible.

Fig. 7: All functions and setting data of the complex conveying and dosing machine are controlled by CONTROLnet, an integrated control concept for the operation, monitoring and management of all steps of raw material handling and connnected to the motan master computer system via LINKnet 2.0.

Success due to many years of proven partnership

Finally, in his résumé of the project process, Helmut Reckziegel sums up the main criterion for the stable production after only a short start‑up phase: “In view of the introduction to a new dimension of mass production, it was important for us to keep the technical risk at a small, manageable level. It is not least for this reason, therefore, that we decided to continue our long‑standing, proven partnerships. We have been working with Luger, the systems technology partner of motan, for more than 40 years already. We knew from similar machine projects in the past that the motan‑components would not call into question the availability of the complete system of 90 per cent required by us around the clock. Likewise, we assumed that the necessary dosing accuracy and the full integration of all setting and performance specifications would also be given in our “big data concept” for the logging of quality data.” (Fig.8)

Fig. 8: Helmut Reckziegel, Head of Business Unit Capsules at Greiner Packaging and Horst Bar, the responsible Project Manager at Luger GesmbH look back on 40 years of co-operation with motan.

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