Cast Film Dies and Auxiliary Equipment, 2000 Polymers, Laminations & Coatings Conference Proceedings
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Typically, when we refer to a cast film die we prefer to address it as part of a die system because of the synergistic effect of all the components. Proper melt delivery through capillary pipes, combining adapter in the case of coextrusion, and spreading and thinning in the die all contribute to the quality of the extrudate.
Having created a good quality melt in the extruder, we want to deliver the same quality melt through the melt transfer pipes. These capillary pipes or adapters should neither add nor remove excessive heat from the melt stream. Melt transfer pipes should be of substantial mass to maintain uniform temperature, and heated appropriately to the melt temperature of the polymer they are conveying (Fig. 2). To correctly size a melt pipe you must balance pressure drop and residence time, often not an easy task. The longer the transfer pipe, the greater the pressure drop. Simply increasing the pipe inside diameter will reduce pressure drop, but at the expense of increased residence time.