Strictly-Extrusion

Nova Chemicals, USA, has introduced its Styrosun weather-resistant HIPS in North America. Styrosun is available in extrusion and injection molding grades and is produced by Nova in Breda, the Netherlands. The company has created a weather-resistant polymer that reduces breakdown and discoloration by modifying high-impact polystyrene. Data collected from an extensive Alpine outdoor- weathering test reveals that uv-stabilized ABS and standard uv-stabilized HIPS experienced twice as much yellowing from uv rays as Styrosun. In addition, the impact retention of Styrosun is much better than other styrenic polymers and similar to inherently weatherable ASA. Styrosun is currently used in numerous outdoor applications, including telecommunications equipment, transportation and recreational vehicles, household appliances, placards and billboards, and building and construction elements. In addition, applications continue to grow in wood replacement for outdoor decking, porch railings, and decorative molding.

An innovative flat die design originally developed to stop melt leakage at the deckled portions of the die gap in extrusion coating now provides the same benefits for cast film, according to Extrusion Dies, Inc. (EDI).

Leakage has been a persistent problem with deckles, which are movable barriers at both ends of the die that enable operators to change product width for each job run. EDI’s new system combines an internal deckle (which blocks flow with blades between the die lips) and an external deckle (which seals off the die gap from outside). “Because the external deckle is linked to the drive of the internal deckle, the units function as one system, providing precisely coordinated movement and a truly leak-proof barrier,” said Sam G. Iuliano, Manager of Technical Sales.

External deckles provide more effective seals than internal deckles, whose main advantage is their more streamlined diversion of melt flow. While the external deckle in the coating version of EDI’s new system covers both die lips, for the film version EDI has developed one that mounts only on the flexible-lip side of the slit, leaving the fixed-lip side unobstructed to ensure that the air gap necessary between lips and casting roll is not compromised.

“The streamlining achievable with an internal deckle is even more important for cast film than for coatings, which are more ‘forgiving’ of hang-ups or dead spots in melt flow,” said Iuliano. “In cast film, the polymer degradation caused by such flow disruptions can cause serious optical defects and degrade physical properties.”

New System Design Acknowledges Real-World Practice of Many Operators
“Even though the melt pressure behind a deckle can be very high, a well-designed deckle should be leak-proof if the operator fully tightens the lip-adjusting bolts at each product changeover,”
said Iuliano. “In the real world, however, operators often do not tighten the bolts fully, opting instead for a torque level that allows blade movement without need for loosening and retightening the bolts.”

EDI provides the new dual-deckle system with a motorized drive or a manual one operated by means of a hand-wheel.