Cast MDO technology: Cost-effective production of fully recyclable, highly transparent packaging with and without barriers
With the use of a stretching unit, the primary film produced in an extrusion line is heated in a further process step, stretched in the machine direction, and then cooled again precisely. The polymer molecule chains in the individual layers of the film are oriented in the longitudinal direction. This gives the resulting stretched secondary film properties that enable it to be used, for example, as a laminating or printing carrier film, improves properties such as barrier and stiffness, and thus increases the quality of packaging and efficiency in further processing.
While the use of MDO technology in the production of blown films is more widely established, its use in the flat film market is only just gaining momentum. "We are convinced that the market for MDO flat films will grow significantly. After all, the demand for recyclable mono-material films is increasing, and the cast process offers unique advantages that are relevant for many manufacturers," says Tino Laue, Product Manager Barrier Film and Sheet at Reifenhäuser Cast Sheet Coating. One example of the special properties of cast MDO films is their high transparency and excellent flatness. These effects are due to the cooling process on a casting roller. Due to the efficient cooling on the water-tempered casting roll, very fine and uniform crystalline structures are formed in the film. This gives cast MDO films excellent optical properties. Precise cooling and fixation on the casting roll also enable very good thickness tolerance and flatness in MDO cast films, which are crucial for problem-free further processing.
Reifenhäuser Cast MDO stretching process
The main process steps in Cast-MDO:
- Extrusion: Forming a cast film without exceeding the melting temperature of the polymer.
- Shock cooling: The cast film, which is still hot, is formed through the die gap of the flat die, then passes onto a casting roller and is cooled abruptly and precisely. This process prevents the formation of coarse crystalline structures in the primary film. This gives the film a fine crystalline structure.
- Stretching zone: The primary film enters the precisely temperature-controlled stretching zone, where it is softened and stretched in the machine direction. The molecular chains orient themselves in the longitudinal direction, which improves the mechanical and optical properties of the film.
- Annealing zone: The film relaxes in this area. The tensions in the material are reduced and the oriented molecular chains stabilize. This prevents the film from shrinking more than intended during further processing and losing its flatness.
- Edge trimming: The stretching process results in a constriction effect, which leads to thicker edge areas. In the case of flat films, these are cut off and returned directly to the main extruder and thus to the production process in an energy-efficient and material-friendly manner without prior regranulation.
- Winder: After cooling, the secondary film, which is now ready for further processing, is rolled up on the winder.
Cast-MDO is economical, resource-efficient, and provides a good barrier effect.
Another huge advantage for line operators is that Cast-MDO produces hardly any production waste due to neck-in. The thicker edge areas resulting from the stretching process must be cut off, but if they are of the same type, they can be immediately fed back into the main extruder and thus back into the production process. If additional barrier layers, e.g., made of EVOH or other incompatible materials, are contained in the film, the innovative encapsulation technology from Reifenhäuser Cast Sheet Coating comes into play. This ensures that these barrier layers do not penetrate into the edge area in symmetrical composites. On the one hand, this means that the edges made of PP or PE can be easily reprocessed and no high-priced barrier material is wasted.
MDO technology is ideal for improving the barrier properties of flat films. This is because the films have a compacted and oriented molecular structure in the machine direction, which makes it much more difficult for gas and water molecules in particular to penetrate – ideal for all packaging that is designed to protect flavors or ensure a long shelf life and freshness of the packaged product. Special raw materials in the layer structure, such as EVOH, can further increase the barrier effect during gas exchange. Stretching the film allows the EVOH layer thickness to be reduced, which saves on expensive raw materials while maintaining or even improving the barrier effect. Films produced in this way are truly versatile and are used as packaging material for food, but also for household chemicals or in technical films where protection against moisture, low gas exchange, or aroma loss is important. This ensures their functionality and guarantees shelf life.
Advantages thanks to Cast-MDO:
- Improved transparency thanks to finer crystallinity
- Highly precise thickness tolerance and good flatness
- Production of PP- and PE-based films with and without functional barriers for a wide range of monomaterial applications
- Less material usage, even with high-priced barrier material
- High efficiency thanks to internal recycling of edge trimmings.
When developing its Cast-MDO technology, Reifenhäuser CSC always had further processing capabilities in mind. “This is the only way to make the technology relevant,” emphasizes Laue. “We went back from the product to the machine in order to take consumer benefits and the concerns of further processors into account. This ensures that our customers can use the MDO processes without major adjustments and achieve the required product quality.”
Predictable demand due to optical properties and recycling advantages
It is already clear today that investing in cast MDO systems is likely to pay off for flat film manufacturers. “Consumers in Asia, for example, appreciate good visual properties in packaging. Companies are therefore keen to set themselves apart from the competition through the quality of their packaging material, as enabled by MDO,” says Sofija Bertasa from the Technical Sales Team at Reifenhäuser Cast Sheet Coating. Customer convenience is evident in reusable stand-up pouches. Cast MDO gives them an “easy tear” effect. This allows pouches to be opened in one direction, as if pulled along a ruler. They can then be resealed using internal clips or zippers.
Such convenient packaging is also in demand in Europe. In addition, European Union regulations are likely to bring about changes to which Cast-MDO has the answer. “In the area of recycling in particular, the Packaging Waste Regulation aims to integrate more plastic products into the circular economy and, from 2030, to allow only monomaterial packaging, for example made of PP or PE,” says Sofija Bertasa. "Cast-MDO enables the production of recyclable film packaging that is sorted by type. " And if higher barrier properties are required, stretching the films in the Cast-MDO process allows the EVOH content to be less than five percent of the total weight of the packaging – up to this limit, materials are considered recyclable monomaterials. The first international brand owners are already increasing the proportion of their recyclable packaging.
Easy handling and quick product changes
Despite the advantages in terms of recycling and product properties, there are still reservations about MDO technology in the industry: the process could be more difficult for operators to handle and therefore inefficient. Tino Laue can reassure manufacturers: "With the Cast-MDO process, our customers benefit from the high degree of automation in Reifenhäuser systems: all process settings and recipes can be reproduced at the touch of a button. In addition, PAM automation for the die and coextrusion adapter enables quick and operator-independent recipe, thickness, and width changes." These features make quick product changes a breeze, even when producing with MDO technology—a real competitive advantage in times of increasing skilled labor shortages.
Retrofitting MDO technology and Reifenhäuser expertise
As a rule, cast lines from all suppliers can be retrofitted with Reifenhäuser CSC's MDO technology, as long as the maximum width of the MDO does not exceed 3.60 meters. The system includes a measuring system for thickness control of the secondary film after the MDO, while a heating and cooling unit keeps the rolls extremely stable and precisely tempered. An optimal process window must be found for stretching the film, which must be tailored to the respective polymer formulation. If the temperature is too high, the polymer could melt; if it is too low, tension would remain in the film. “We use water in the rolls to ensure stable process conditions during temperature control. This allows us to maintain the specified temperatures with extreme precision,” says Tino Laue.
The experts at Reifenhäuser Cast Sheet Coating are happy to advise their customers on all aspects of MDO technology and the right process settings. In addition, they conduct tests in the company's own technical center to determine the polymer formulations that are perfectly matched to the MDO process and the customers' markets. With this holistic approach, Reifenhäuser supports companies from the development of ideas to the finished product. Even when it comes to entering the market as a newcomer, Reifenhäuser provides support with its expertise and extensive network in the industry.
Would you also like to benefit from the advantages of MDO technology for cast films? Then get in touch with us. We will be happy to advise you on planning and implementation:
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