Blown Film Stack Die Cuts Thickness Variation.

An unusual stack-die concept that was first discussed at NPE '97 is just now becoming commercially available. The patent-pending "Redi" (regular division) die comes from Addex Inc. USA, Hingham, Mass. It splits the melt stream into two, then four, eight, and finally 16 channels. When the melt reaches 16 ports, it turns to the center like spokes on a wheel, with every other port pointing up or down. The melt branching occurs in a vertical plane around the outer circumference of the die, thus avoiding pressure build-up between the plates. This reportedly eliminates the size limitations affecting some other stack dies.

The die plates are mirror images, offset by half the distance between ports. Melt flows in spirals toward the lip, creating a sine-wave profile in which a high-flow area meets a low-flow area. This yields 20% less thickness variation than with a spiral-mandrel die, Addex says. It will present details on the die at the Flex-Pak Americas 2000 conference in Chicago in March, sponsored by Schotland Business Research, Skillman, N.J.