New Process Extrudes UHMW-PE Blown Film

A novel process that combines compression molding and blown film extrusion produces thin, biaxially oriented blown film out of ultra-high-molecular-weight PE without plasticizers.

A novel process that combines compression molding and blown film extrusion produces thin, biaxially oriented blown film out of ultra-high-molecular-weight PE without plasticizers. The process was presented at this year’s SPE ANTEC meeting by Takashi Nakahara of Mitsui Chemicals of Japan (U.S. office in Purchase, N.Y.). Mitsui supplies UHMW-PE under the name Hi-Zex Million. Its blown film process uses machinery built by Tomi Machinery Manufacturing Co., Yokohama, Japan. A long, single-screw extruder with shallow flights, grooved barrel, and more than 30:1 L/D compresses resin powder tightly in the heated barrel until the boundaries of the particles disappear. This hot, viscoelastic solid then goes into a rotating crosshead die with a single flight at the bottom, which forces the melt over a rotating, heated mandrel that forms it into a tubular shape. The mandrel repairs any adhesion flaws from extrusion, so the pipe can be blown into film without bursting. With this apparatus, UHMW-PE is blown with MD stretch ratios from 6:1 to 30:1 and BUR from 6:1 to 10:1, yielding thicknesses of 5 to 140 microns. Its extremely high tensile strength and abrasion resistance suggest applications in industrial film liners and coverings for hydraulic hoses. Until now, UHMW-PE film could be made only by skiving off a compression-molded block, which is slow and costly and can’t make film thinner than about 50 microns. The new process is continuous with potentially high output—the test line makes 1.5-meter layflat film at over 100 lb/hr. Properties are even better than those of skived film (see table).