A new customized nine-extruder, five-layer sheet extrusion system for production of multi-colored, striped sheet for thermoformed HIPS yogurt cups is said to be one of the most unusual and sophisticated packaging sheet lines on the market. Supplied by Welex Inc., Blue Bell, Pa., the system produces sheet up to 60 in. wide in a thickness range of 0.020 to 0.060 in. at a rate of 3000 lb/hr. The novel system was shipped to a leading European custom sheet manufacturer earlier this year.
The nine extruders are 2.5-in. and 3.5-in., 30:1, vented, air-cooled versions with two-stage screws. The five-layer sheet construction includes a crystal PS gloss layer, a five-color (custom-configurable) stripe layer, a white layer, a scrap foam layer, and a white bottom layer. The scrap foam layer is produced via a proprietary gas-injection process. Each mobile-mounted extruder includes a slide-plate screen changer and gear pump for high-precision output. The system can also run PP with no equipment changes.
Welex Sentinel color touchscreen modular control interfaces are incorporated into each extruder and the sheet take-off. Sheet profile is monitored by a Scantech x-ray gauging system, which controls the Welex Autoflex die with thermal-expansion bolts. The line also features the Welex Evolution sheet takeoff with individual roll drive. It boasts automatic roll-gap controls and a set of driven, water-cooled secondary cooling rolls to assure uniform sheet temperature at the end of the line prior to winding onto jumbo rolls.