January 2007

Colines® blown film systems

Colines® Extrusion recently commissioned (see newsletter no.6) a new 5-layer BARRIERBLOWN® line with a re-designed die, that offers a major step forward in rheology. From the outset it was clear that the design goals had to be: further reduction of the thermal mass and physical dimensions (thus saving energy and building height); improve the flow characteristics and reduce residence times; increase the flexibility in processing resins of fundamentally different nature; enhance the individual layer tolerances. The result is an outstanding tool, which fulfills the expectations better than previewed. The obtained tolerances can be considered amongst the best in the industry, on par with the guarantees claimed by other manufacturers. The same end effects are to be taken for granted for the 7-layer blown film die, where layers of two micron thickness are feasible under optimum conditions. Availing ourselves of the same, undisputed experts that were responsible for the successful barrier blown-film die, Colines® Extrusion has set out to design a complete range of 3-layer dies for mostly high end blown-film applications. Where in case of the barrier film dies the accent is mostly on quality and not so much on volume, the 3-layer dies (and the 5-layer dies for non-barrier applications) will be designed around both high flow rates and quality. For obvious reasons the quality needs to be maintained, since high quality does fetch slightly better prices, even in the difficult commodity markets. However, high production rates do have a very positive impact when it comes to cutting down the per-weight-unit cost of producing films, so ample attention will be dedicated to this aspect. High quality and high quantity are definitely not in contradiction with each other. Both can be obtained in the same die, provided they are designed in from the beginning. It all has to do with shear rates and pressure drop of the resin melts on their way to the die lip. In simple wording, a die designed for high flow rates will not yield good films at low flow rates, owing to the rheological characteristics of the melt. On the other hand, if one tries to push the output on a die that was not designed for this purpose, the resins will suffer badly in view of the higher shear rates. They will overheat, degrade and produce very poor overall thickness tolerances, mechanical characteristics, etc., phenomena often experienced by many. The newly designed IBC air passages for the 5-layer BARRIERBLOWN® die offer more than enough breathing space to allow for a very high air exchange rate that, in combination with an excellent air ring design, is needed to cool down important volumes of films of various nature. Depending on customer requirements and preferences, the new range of 3—layer dies will be available with a gauge tolerance control system based on heater cartridges integrated in the external die lip, or they can be delivered with a standard female die lip to allow the end-user to employ a gauge tolerance control system incorporated into the air ring design. Colines® plans to manufacture a first complete 3-layer POLYBLOWN® line in 2007, which will then be available for interested parties to view in operation. Our readers will of course be informed of this event through our newsletter system and information bulletins from our local representatives.