The market for flexible food packaging is booming, and at the same time competition between manufacturers is increasing. These rely on efficient production processes with which they can manufacture packaging products in the required shape and quality. For example, multilayer thermoforming sheets should be transparent and easy to form. "For these properties, it is important to keep the crystallinity of the film as low as possible," explains Max Herchenbach, Senior Product Manager Aqua Cool at Reifenhäuser. But this requirement is a challenge in the production of typical barrier films: The more time it takes a film to cool down, the more it crystallizes and loses its formability and transparency in the process. "Manufacturers of air-cooled blown films often counteract this process by using copolymers. However, these are significantly more expensive than the standard raw materials and reduce the profitability of production. ", explains Herchenbach. Instead, producers can use water-cooled blown film lines with shock cooling. This makes it possible to produce highly transparent film at lower raw material costs, which is excellent for thermoforming.
How does water shock cooling work?
Water cooling turns blown film extrusion on its head: following the force of gravity of the water, the extrusion direction from the die runs from top to bottom. The bubble is first inflated to the required format and then passes through the EVO Ultra Quench water cooling and vacuum calibration chamber, where as much heat as possible is extracted from it by water contact. The vacuum in the cooling chamber also provides the necessary hold and ensures that the film leaves the cooling chamber almost dry.
How much faster does the film cool down compared to air cooling?
The EVO Aqua Cool blown film line from Reifenhäuser cools the melt much faster than an air-cooled blown film line because the cooling capacity of water is higher than that of air. The film is also cooled very soon after leaving the blow head. Whereas in the air-cooled blown film system the distance between the die and the film take-off is needed for cooling, in the water-cooled system the bubble enters the cooling chamber shortly after leaving the die. There it is then cooled down in a shock-like manner.
What properties does the film acquire as a result of the abrupt cooling?
The rapid cooling of the melt inhibits or even prevents crystallization. This keeps the barrier film transparent and glossy, gives it higher puncture and tear resistance and excellent forming properties. The film also exhibits a softer feel and a high-quality appearance. In addition, asymmetrical structures, i.e. multilayer films made of different material classes, are easier to process on downstream machines thanks to a very low curl.
However, water cooling not only improves film properties - it also saves material and thus raw material costs: Thanks to water cooling, the particularly high-performance film layers can be designed thinner, which means that less raw material is required. Or manufacturers can use cheaper raw materials while maintaining the same film properties, because they can use homopolymers instead of more expensive copolymers, for example. "Depending on the raw material and layer structure, different levels of savings are possible here," explains Herchenbach. For example, PA homopolymers cost around 1 euro less per kilogram on average than PA copolymers.
EVO Aqua Cool fact sheet for barrier films
Barrier films produced on an EVO Aqua Cool blown film line from Reifenhäuser are particularly suitable for special applications in the food sector. For example, their formability makes them ideal for thermoforming films and vacuum skin packs, or their optical properties make them suitable for vacuum pouch packaging or lidding films.
"However, whether a water-cooled blown film line is the right line technology for the application also depends on the output the producer is aiming for and the flexibility and product range he needs," says Herchenbach. "Depending on the case, an air-cooled blown film line or a cast line may be a better fit. Within the Reifenhäuser Group, we offer the entire range of lines and advise our customers on the right technology for their requirements."
Would you like to know whether an EVO Aqua Cool blown film system fits your requirements? Then please feel free to contact us.