Until recently, manufacturing biaxially oriented polyester film (BOPET) was commonly based in two-step technology. Step one was to produce the polyester resin as pellets, and step two was to convert those pellets into BOPET film by extrusion and subsequent film casting and stretching. The direct film casting technology (DFC) combines economy of scale with a significant simplification of the processing. Plastics spoke with Ludwig Eckart, COO Sales & Project Management, Brückner Maschinenbau, Siegsdorf, Germany, on DFC lines, its technology and its markets.
Hitherto, a single BOPET line of more than 100t/day based on extrusion technology was the standard technology in use on a world scale. Now a poly-condensation plant of up to 600t/day can be directly connected, for instance, to four or six film casting and stretching lines. A prerequisite for this important step is the high performance, efficiency, consistency and reliability of casting and film stretching technology executed and developed by Brückner Maschinenbau of Germany.
In January 2013 the major Chinese film producer Jiangsu Shuangxing Color Plastic New Materials and Brückner Maschinenbau rang in a new era by commissioning four large-scale DFC lines with a total annual output of more than 125,000t/year. All these four lines started extremely smoothly and since then have been reliably producing high quality film for the market.
Plastics:Could you please describe a DFC plant layout in simple terms?
Eckart: The majority of common film stretching lines for BOPET, BOPP, BOPA or any other raw material have an extrusion system for melting the resin. By applying direct film casting technology the main extruder is made obsolete, because the poly-condensation plant is connected via the polymer melt line directly to the melt pump and die of the film stretching line.
The polymer melt remains in its original condition – that means absolutely oxygen-free. The quality of melt from a polymerisation plant is better and also more stable than anything an extrusion system can provide. That results in improved film quality and a higher annual yield from film production lines.
Plastics: What are the challenges and key features of this technology?
Eckart: I would say that one of the key features is of course the interface between the poly-condensation plant and the stretching line. For example, it is vital that film producers have the possibility to process with a continuous volume flow rate regardless of any changes in the stretching process.
But DFC is not only about the integration of the poly-condensation and stretching process. The greatest challenge in such a project is to ensure enough flexibility for the production of various film types. And to make sure that the different quality requirements are constantly met – in order to satisfy not only our customers but also the markets. Thanks to their sophisticated process automation our lines ensure flexibility when it comes to product changes and guarantee a constant quality of the different films.
Plastics: What are common plant and line capacities?
Eckart: Today’s projects comprise four to eight lines with an annual output of 30,000 to 40,000t each, adding up to a total output of between 120,000 and approximately 300,000t/year.
Plastics: Mr Eckart, what are the reasons for deciding to implement DFC technology?
Eckart: Within highly competitive BOPET markets, DFC technology gives film producers a number of advantages: lower energy consumption and considerable savings in transport, logistics and personnel costs – resulting in a clear reduction of the overall production costs.
Plastics: Where are the new, large-scale DFC projects located?
Eckart: Up to now we have sold four complete projects to China with a total of 20 production lines. This is not surprising because Chinese BOPET film capacities have been continuously extended over the years and the markets are really competitive. Therefore not only experienced BOPET film producers but also newcomers with a strong background in polymer technology, particularly within the textile industry, are now investing in industrial-scale DFC projects in order to gain a competitive edge through the benefits of DFC: efficiency, productivity and profitability.
Plastics: Who is responsible for the melt phase poly-condensation of PET?
Eckart: Our Chinese projects are characterised by a clear division of responsibility: the poly-condensation supplier is responsible for the melt quality, and we take care of the subsequent casting and stretching process. Of course it is vital for the success of the whole project that the interface is properly defined and that the automation of both the poly-condensation and the stretching line are perfectly harmonised.
Plastics: Can you describe other highlights within Brückner’s BOPET technology?
Eckart: In recent years we were able to convince the BOPET packaging film industry by means of a number of trend-setting features. To name but a few: an energy-saving twin screw extrusion system without pre-drying for utmost flexibility; our unique multi-gap MD stretching with stretch ratios up to and above 4.5, ensuring enhanced mechanical film properties, high speeds and outputs; and our overall optimised line design and layout for maximum energy savings. For the manufacture of finest quality BOPET industrial and optical films in a thickness range up to 400µm, the highlights of our design incorporate our cascade main extrusion system utilising our Barmag technology, or a special MD stretching section for BOPET optical grade in sequential stretching. Of course our simultaneous system based on our LISIM technology is available for the top end optical films with non-contact stretching and adjustable pattern for stretching and relaxing.
Plastics: Thinking about packaging in a broad sense, how do you see this market in general?
Eckart: Worldwide the packaging markets will continue to grow in high single-digit figures. In emerging markets such as China, India, South-East Asia, Russia and Latin America in particular, the reasons for this are evident: the middle class is growing strongly and increasing numbers of people are moving into big cities – and they are buying their goods in supermarkets and shopping malls. These are increasing in number so that more packaged goods are in demand and new distribution channels are being created. And all these factors together mean that the demand for flexible packaging will continue to rise.
Within the flexible packaging sector, biaxially oriented films will continue to show the highest growth rates – simply because of their unrivalled position in providing the highest yield of material used combined with properties such as mechanical strength, good optical appearance, and a high barrier against gases such as oxygen or water vapour, for example in order to increase the shelf-life of the foodstuffs. Various developments relating to the higher functionality of BO films, such as multi-layer or coating technology, will further widen the application window. Virtually no other material better fulfills the high demands of the markets, also with regard to the increasingly important topic of sustainability.
Plastics: What are the next surprises and revolutionary developments in Brückner’s film technology?
Eckart: Our worldwide unique technology centre with its own pilot line for process and technological developments is ideally suited to helping us to develop and offer technological expertise to the market. It permits a wide range of materials to be processed via either sequential or simultaneous stretching, thereby helping us to gain extensive experience over the years. Within the packaging film sector we have made some promising developments, such as transparent seven-layer barrier film with an EVOH layer; bi-axially oriented polyethylene for “low shrink packaging” and biodegradable film made from PLA for packaging, shrink and thermoform applications. Some of these developments are already well positioned in the markets, while others are attracting considerable attention within the value chain.
Bi-axially oriented specialty films are also increasingly being used in technical applications. Fast-growing markets include displays and screens, photovoltaic panels and separator films in high performance lithium ion batteries. These new markets exhibit high growth rates and the demand for new production lines in this sector is on the rise. Driven by political factors such as the trend towards renewable energy in the form of photovoltaic panels or electric mobility, it is possible that we may experience a rapid boom in this sector in the near future. And this is where Brückner offers trend-setting concepts. Just one example: our lines for the production of battery separator films for high performance lithium ion batteries have attracted great interest within the industry. The benefits compared with the self-made, specially tailored machines which were previously widely used are higher productivity, economic efficiency, a consistent film quality and a reduced environmental impact. We have already sold two of these lines and there are more to come.
Plastics: Thank you very much.
Author: Dr. Ulrich K. Thiele